java.lang.AssertionError on JDK 12 when using nested lambda expressions

A DESCRIPTION OF THE PROBLEM :
During compilation with jdk-11.0.2 javac fails with:

$ javac jdkassertionbug/JdkAssertionBug.java
An exception has occurred in the compiler (11.0.2). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$2$1.setOverloadKind(DeferredAttr.java:172)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.visitReference(ArgumentAttr.java:283)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMemberReference.accept(JCTree.java:2190)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.attribArg(ArgumentAttr.java:197)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:653)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribArgs(Attr.java:751)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1997)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr.attribSpeculative(DeferredAttr.java:498)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr.attribSpeculative(DeferredAttr.java:481)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.lambda$processArg$0(ArgumentAttr.java:220)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.processArg(ArgumentAttr.java:242)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.processArg(ArgumentAttr.java:219)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.visitApply(ArgumentAttr.java:307)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.attribArg(ArgumentAttr.java:197)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:653)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribArgs(Attr.java:751)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1997)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:702)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1773)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1452)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitLambda(Attr.java:2598)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCLambda.accept(JCTree.java:1807)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$4.complete(DeferredAttr.java:374)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:335)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:321)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$MethodResultInfo.check(Resolve.java:1060)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.checkArg(Resolve.java:887)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$AbstractMethodCheck.argumentsAcceptable(Resolve.java:775)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.argumentsAcceptable(Resolve.java:896)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.rawInstantiate(Resolve.java:618)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.checkMethod(Resolve.java:644)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:4120)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3913)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3814)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkId(Attr.java:3803)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitSelect(Attr.java:3696)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:2110)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:2006)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:702)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1773)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1452)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitLambda(Attr.java:2598)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCLambda.accept(JCTree.java:1807)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$4.complete(DeferredAttr.java:374)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:335)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:321)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$MethodResultInfo.check(Resolve.java:1060)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.checkArg(Resolve.java:887)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$AbstractMethodCheck.argumentsAcceptable(Resolve.java:775)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.argumentsAcceptable(Resolve.java:896)
        at jdk.compiler/com.sun.tools.javac.comp.Infer.instantiateMethod(Infer.java:181)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.rawInstantiate(Resolve.java:605)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.checkMethod(Resolve.java:644)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:4120)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3913)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3814)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkId(Attr.java:3803)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitSelect(Attr.java:3696)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:2110)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:2006)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitReturn(Attr.java:1866)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCReturn.accept(JCTree.java:1546)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:1294)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1020)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:1098)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:866)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4683)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4574)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4503)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attrib(Attr.java:4448)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1341)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:973)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:311)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:170)
        at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:57)
        at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:43)

The same code works on jdk1.8.0_202.

REGRESSION : Last worked in version 8u202

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the attached code with jdk-11.0.2 on Windows 10. AssertionError is thrown during compilation.

The failing row is:

stringList.forEach(localString -> { ... }

Changing to a for loop constuct will fix the issue:

for (String localString: stringList) { ... }

Both constructs work on jdk8.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Code should compile or give an understandable error message.
ACTUAL -
javac fails with AssertionErrror:

$ javac jdkassertionbug/JdkAssertionBug.java
An exception has occurred in the compiler (11.0.2). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$2$1.setOverloadKind(DeferredAttr.java:172)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.visitReference(ArgumentAttr.java:283)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMemberReference.accept(JCTree.java:2190)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.attribArg(ArgumentAttr.java:197)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:653)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribArgs(Attr.java:751)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1997)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr.attribSpeculative(DeferredAttr.java:498)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr.attribSpeculative(DeferredAttr.java:481)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.lambda$processArg$0(ArgumentAttr.java:220)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.processArg(ArgumentAttr.java:242)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.processArg(ArgumentAttr.java:219)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.visitApply(ArgumentAttr.java:307)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.ArgumentAttr.attribArg(ArgumentAttr.java:197)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:653)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribArgs(Attr.java:751)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1997)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:702)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1773)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1452)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitLambda(Attr.java:2598)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCLambda.accept(JCTree.java:1807)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$4.complete(DeferredAttr.java:374)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:335)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:321)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$MethodResultInfo.check(Resolve.java:1060)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.checkArg(Resolve.java:887)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$AbstractMethodCheck.argumentsAcceptable(Resolve.java:775)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.argumentsAcceptable(Resolve.java:896)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.rawInstantiate(Resolve.java:618)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.checkMethod(Resolve.java:644)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:4120)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3913)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3814)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkId(Attr.java:3803)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitSelect(Attr.java:3696)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:2110)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:2006)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:702)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1773)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1452)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitLambda(Attr.java:2598)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCLambda.accept(JCTree.java:1807)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$4.complete(DeferredAttr.java:374)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:335)
        at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:321)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$MethodResultInfo.check(Resolve.java:1060)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.checkArg(Resolve.java:887)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$AbstractMethodCheck.argumentsAcceptable(Resolve.java:775)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve$4.argumentsAcceptable(Resolve.java:896)
        at jdk.compiler/com.sun.tools.javac.comp.Infer.instantiateMethod(Infer.java:181)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.rawInstantiate(Resolve.java:605)
        at jdk.compiler/com.sun.tools.javac.comp.Resolve.checkMethod(Resolve.java:644)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:4120)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3913)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3814)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.checkId(Attr.java:3803)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitSelect(Attr.java:3696)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:2110)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:2006)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitReturn(Attr.java:1866)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCReturn.accept(JCTree.java:1546)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:1294)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1020)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:1098)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:866)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4683)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4574)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4503)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attrib(Attr.java:4448)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1341)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:973)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:311)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:170)
        at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:57)
        at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:43)


---------- BEGIN SOURCE ----------
package jdkassertionbug;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.function.Supplier;

public class JdkAssertionBug {

    private Supplier<CompletableFuture<String>> stringSupplier;

    private Supplier<CompletableFuture<List<String>>> stringListSupplier;

    public JdkAssertionBug() {
        stringListSupplier = () -> new CompletableFuture<>();
    }

    public CompletableFuture<List<String>> testCaseFailing() {

        return stringListSupplier.get().thenApply(stringList -> {
            List<CompletableFuture<Void>> futures = new ArrayList<>();
            stringList.forEach(localString -> {
                futures.add(
                        stringSupplier.get().thenAccept(localString::equals)
                );
            });
            return stringList;
        });
    }

    public CompletableFuture<List<String>> testCaseWorking() {

        return stringListSupplier.get().thenApply(stringList -> {
            List<CompletableFuture<Void>> futures = new ArrayList<>();
            for (String localString: stringList) {
                futures.add(
                        stringSupplier.get().thenAccept(localString::equals)
                );
            }
            return stringList;
        });
    }

    public static void main(String[] args) {
        JdkAssertionBug bug = new JdkAssertionBug();
        System.out.println("This compiles and works on jdk1.8.0_202: " + bug.testCaseWorking());
        System.out.println("This compiles and works on jdk1.8.0_202 but fails compile on jdk-11.0.2: " + bug.testCaseFailing());
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use a for loop instead of a lambda constuct.

FREQUENCY : always