Consider this code:
---
class Test {
    void test() {
        cand((var s, t) -> \"\");
    }
    void cand(I i) { }
    interface I { public String test(String s); }
}
---

Using Trees.getScope to get a Scope for the lambda body leads to:
---
java.lang.NullPointerException
at jdk.compiler/com.sun.tools.javac.code.Types.subst(Types.java:3269)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.asUndetVar(InferenceContext.java:207)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.asUndetVars(InferenceContext.java:213)
at jdk.compiler/com.sun.tools.javac.comp.Attr.checkLambdaCompatible(Attr.java:2892)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitLambda(Attr.java:2629)
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:667)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr.attribSpeculative(DeferredAttr.java:501)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr.attribSpeculative(DeferredAttr.java:484)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$4.complete(DeferredAttr.java:372)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:338)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredType.check(DeferredAttr.java:324)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$RecoveryDeferredTypeMap.recover(DeferredAttr.java:1084)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$RecoveryDeferredTypeMap.typeOf(DeferredAttr.java:1055)
at jdk.compiler/com.sun.tools.javac.comp.Resolve$ResolveDeferredRecoveryMap.typeOf(Resolve.java:2564)
at jdk.compiler/com.sun.tools.javac.comp.Resolve$ResolveDeferredRecoveryMap.typeOf(Resolve.java:2556)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredTypeMap.visitType(DeferredAttr.java:1022)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$RecoveryDeferredTypeMap.visitType(DeferredAttr.java:1045)
at jdk.compiler/com.sun.tools.javac.comp.DeferredAttr$DeferredTypeMap.visitType(DeferredAttr.java:1008)
at jdk.compiler/com.sun.tools.javac.code.Type.accept(Type.java:214)
at jdk.compiler/com.sun.tools.javac.code.Types$MapVisitor.visit(Types.java:4951)
at jdk.compiler/com.sun.tools.javac.code.Types$TypeMapping.apply(Types.java:4962)
at jdk.compiler/com.sun.tools.javac.code.Types$TypeMapping.apply(Types.java:4960)
at jdk.compiler/com.sun.tools.javac.util.List.map(List.java:425)
at jdk.compiler/com.sun.tools.javac.comp.Resolve$8.getArgumentTypes(Resolve.java:2552)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.accessInternal(Resolve.java:2473)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.accessMethod(Resolve.java:2493)
at jdk.compiler/com.sun.tools.javac.comp.Resolve$BasicLookupHelper.access(Resolve.java:3307)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.lookupMethod(Resolve.java:3548)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.lookupMethod(Resolve.java:3528)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.resolveMethod(Resolve.java:2618)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitIdent(Attr.java:3504)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:2243)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:667)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:2022)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:667)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:718)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1789)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1452)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:667)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:740)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:759)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:1310)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1020)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:667)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:740)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStatToTree(Attr.java:426)
at jdk.compiler/com.sun.tools.javac.api.JavacTrees.attribStatToTree(JavacTrees.java:937)
at jdk.compiler/com.sun.tools.javac.api.JavacTrees.getAttrContext(JavacTrees.java:911)
at jdk.compiler/com.sun.tools.javac.api.JavacTrees.getScope(JavacTrees.java:785)
at jdk.compiler/com.sun.tools.javac.api.JavacTrees.getScope(JavacTrees.java:165)
---