oops; need method: add getChildren() method to Tree.

runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java

@@ -193,6 +193,11 @@ public class ParserRuleContext extends RuleContext {
 		return null;
 	}
 
+	@Override
+	public List<? extends ParseTree> getChildren() {
+		return children;
+	}
+
 	public TerminalNode getToken(int ttype, int i) {
 		if ( children==null || i < 0 || i >= children.size() ) {
 			return null;