if the following code is compiled with -g:

public class Test2 {
    protected int getLineNumberWidth() {
        int newWidth = 0;
        String tc = "b";
        if (tc != null) {
            String fm;
            if (tc.trim() != null) {
            } else if ((fm = "b") != null) {
                newWidth += fm.length();
            }
        }

        return newWidth;
    }
}

you get:

java.lang.AssertionError
        at com.sun.tools.javac.util.Assert.error(Assert.java:126)
        at com.sun.tools.javac.util.Assert.check(Assert.java:45)
        at com.sun.tools.javac.jvm.ClassWriter.writeCode(ClassWriter.java:1190)
        at com.sun.tools.javac.jvm.ClassWriter.writeMethod(ClassWriter.java:1110)
        at com.sun.tools.javac.jvm.ClassWriter.writeMethods(ClassWriter.java:1602)
        at com.sun.tools.javac.jvm.ClassWriter.writeClassFile(ClassWriter.java:1692)
        at com.sun.tools.javac.jvm.ClassWriter.writeClass(ClassWriter.java:1620)
        at com.sun.tools.javac.main.JavaCompiler.genCode(JavaCompiler.java:755)
        at com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1554)
        at com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1518)
        at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:910)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:869)
        at com.sun.tools.javac.main.Main.compile(Main.java:523)
        at com.sun.tools.javac.main.Main.compile(Main.java:381)
        at com.sun.tools.javac.main.Main.compile(Main.java:370)
        at com.sun.tools.javac.main.Main.compile(Main.java:361)
        at com.sun.tools.javac.Main.compile(Main.java:56)
        at com.sun.tools.javac.Main.main(Main.java:42)

(problem discovered by Jan Lahoda)