In certain situations javac with -source 1.5 throws an assertion instead of reporting an error when the last sub-expression of a ternary expression is of type void. Also if the condition is a constant true, no error is reported. -source 1.4 correctly reports the error.

cat > TriVoid.javac
import javax.swing.*;
class TriVoid {
    static void fn() {
        SpringLayout.Constraints cons1 = null;
        SpringLayout.Constraints cons2 = null;
        cons2.setY(
            1==0 ? Spring.constant(0) : cons1.setY(Spring.constant(0))
        );
    }
}

javac -source 1.4 TriVoid.java

TriVoid.java:7: incompatible types for ?: neither is a subtype of the other
second operand: javax.swing.Spring
third operand : void
            1==0 ? Spring.constant(0) : cons1.setY(Spring.constant(0))
                 ^
1 error

javac -source 1.5 TriVoid.java

An exception has occurred in the compiler (1.5.0-beta). Please file a bug at the Java Developer Connection (http://java.sun.com/cgi-bin/bugreport.cgi) after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.AssertionError
        at com.sun.tools.javac.jvm.Items$Item.load(Items.java:183)
        at com.sun.tools.javac.jvm.Items$Item.coerce(Items.java:227)
        at com.sun.tools.javac.jvm.Items$Item.coerce(Items.java:246)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:803)
        at com.sun.tools.javac.jvm.Gen.visitTypeCast(Gen.java:2011)
        at com.sun.tools.javac.tree.Tree$TypeCast.accept(Tree.java:934)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:801)
        at com.sun.tools.javac.jvm.Gen.genArgs(Gen.java:819)
        at com.sun.tools.javac.jvm.Gen.visitApply(Gen.java:1648)
        at com.sun.tools.javac.tree.Tree$Apply.accept(Tree.java:808)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:801)
        at com.sun.tools.javac.jvm.Gen.visitExec(Gen.java:1596)
        at com.sun.tools.javac.tree.Tree$Exec.accept(Tree.java:725)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:648)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:683)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:669)
        at com.sun.tools.javac.jvm.Gen.genStats(Gen.java:720)
        at com.sun.tools.javac.jvm.Gen.visitBlock(Gen.java:967)
        at com.sun.tools.javac.tree.Tree$Block.accept(Tree.java:531)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:648)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:683)
        at com.sun.tools.javac.jvm.Gen.genMethod(Gen.java:905)
        at com.sun.tools.javac.jvm.Gen.visitMethodDef(Gen.java:841)
        at com.sun.tools.javac.tree.Tree$MethodDef.accept(Tree.java:473)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:648)
        at com.sun.tools.javac.jvm.Gen.genClass(Gen.java:2167)
        at com.sun.tools.javac.main.JavaCompiler.genCode(JavaCompiler.java:321)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:460)
        at com.sun.tools.javac.main.Main.compile(Main.java:584)
        at com.sun.tools.javac.main.Main.compile(Main.java:536)
        at com.sun.tools.javac.Main.compile(Main.java:41)
        at com.sun.tools.javac.Main.main(Main.java:32)