public IntervalSet getExpectedTokens() {
		if (recognizer != null) {
			return recognizer.getATN().getExpectedTokens(offendingState, ctx);
		}

		return null;
	}
Gets the set of input symbols which could potentially follow the
previously matched symbol at the time this exception was thrown.

<p>If the set of expected tokens is not known and could not be computed,
this method returns {@code null}.</p>

@return The set of token types that could potentially follow the current
state in the ATN, or {@code null} if the information is not available.
runtime/Java/src/org/antlr/v4/runtime/RecognitionException.java