java.lang.AssertionError on Ternary operator with decrement

ADDITIONAL SYSTEM INFORMATION :
Windows 7 64 bit / jdk - 12.0.2

A DESCRIPTION OF THE PROBLEM :
When, in the code, there is a ternary operator that operates a decrement on a variable, the compiler crashes.

REGRESSION : Last worked in version 8u221

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
private Long maxNumberOfUnits = null; ---> class variable

public void reduceValues() ---> class method
  {
    maxNumberOfUnits = maxNumberOfUnits == null ? 0L : maxNumberOfUnits--;
   
  }

but the problem appears also if the variable is not a class one, for example:

public void reduceValues() ---> class method
  {
    long test = maxNumberOfUnits == null ? 0L : maxNumberOfUnits--;
   
  }



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
compiling
ACTUAL -
 Compilation failure:
 An exception has occurred in the compiler (12.0.2). 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.
e 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.jvm.Gen.visitVarDef(Gen.java:1053)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:962)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:595)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:630)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:616)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStats(Gen.java:667)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitLetExpr(Gen.java:2300)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$LetExpr.accept(JCTree.java:3026)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:853)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitConditional(Gen.java:1835)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCConditional.accept(JCTree.java:1452)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:853)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitSelect(Gen.java:2241)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:2189)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:853)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitApply(Gen.java:1803)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1709)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:853)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitVarDef(Gen.java:1051)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:962)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:595)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:630)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:616)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStats(Gen.java:667)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitBlock(Gen.java:1067)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1026)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:595)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:630)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genMethod(Gen.java:937)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitMethodDef(Gen.java:900)
         at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:872)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:595)
         at jdk.compiler/com.sun.tools.javac.jvm.Gen.genClass(Gen.java:2345)
         at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.genCode(JavaCompiler.java:756)
         at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1635)
         at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1603)
         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 ----------
public class QuantitiesDto {
private Long maxNumberOfUnits = null;

public void reduceValues()
  {
    maxNumberOfUnits = maxNumberOfUnits == null ? 0L : maxNumberOfUnits--;
   
  }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
if(maxNumberOfUnits == null) {
maxNumberOfUnits = 0L;
}
else {
maxNumberOfUnits--;
}

FREQUENCY : always