@SuppressWarnings({"ThrowableResultOfMethodCallIgnored"})
    @Override
    public RecognitionException getCause() {
        return (RecognitionException)super.getCause();
    }
A problem with the syntax of your antlr grammar such as
 "The '{' came as a complete surprise to me at this point in your program"
tool/src/org/antlr/v4/tool/GrammarSyntaxMessage.java