protected BitSet getConflictingAlts(BitSet reportedAlts, ATNConfigSet configs) {
		if (reportedAlts != null) {
			return reportedAlts;
		}

		BitSet result = new BitSet();
		for (ATNConfig config : configs) {
			result.set(config.alt);
		}

		return result;
	}
Computes the set of conflicting or ambiguous alternatives from a
configuration set, if that information was not already provided by the
parser.

@param reportedAlts The set of conflicting or ambiguous alternatives, as
reported by the parser.
@param configs The conflicting or ambiguous configuration set.
@return Returns {@code reportedAlts} if it is not {@code null}, otherwise
returns the set of alternatives represented in {@code configs}.
runtime/Java/src/org/antlr/v4/runtime/DiagnosticErrorListener.java