public static GrammarAST findOptionValueAST(GrammarRootAST root, String option) {
		GrammarAST options = (GrammarAST)root.getFirstChildWithType(ANTLRParser.OPTIONS);
		if ( options!=null && options.getChildCount() > 0 ) {
			for (Object o : options.getChildren()) {
				GrammarAST c = (GrammarAST)o;
				if ( c.getType() == ANTLRParser.ASSIGN &&
					 c.getChild(0).getText().equals(option) )
				{
					return (GrammarAST)c.getChild(1);
				}
			}
		}
		return null;
	}
Manually get option node from tree; return null if no defined.
tool/src/org/antlr/v4/Tool.java