code: protected String getReferenceName(XExpression expr, ITreeAppendable b) {
  		if (b.hasName(expr))
  			return b.getName(expr);
  		if (expr instanceof XFeatureCall) {
  			XFeatureCall featureCall = (XFeatureCall) expr;
  			if (b.hasName(featureCall.getFeature()))
  				return b.getName(featureCall.getFeature());
  		}
  		return null;
  	}
docs: /* @Nullable