@Override
        public boolean eval(Recognizer<?,?> parser, RuleContext parserCallStack) {
            RuleContext localctx = isCtxDependent ? parserCallStack : null;
            return parser.sempred(localctx, ruleIndex, predIndex);
        }
The default {@link SemanticContext}, which is semantically equivalent to
a predicate of the form {@code {true}?}.
runtime/Java/src/org/antlr/v4/runtime/atn/SemanticContext.java