protected void addContextToParseTree() {
		ParserRuleContext parent = (ParserRuleContext)_ctx.parent;
		// add current context to parent if we have a parent
		if ( parent!=null )	{
			parent.addChild(_ctx);
		}
	}
How to create an error node, given a token, associated with a parent.
 Typically, the error node to create is not a function of the parent.

@since 4.7
runtime/Java/src/org/antlr/v4/runtime/Parser.java