//replace with a new function call, since its argument could be changed.

      call = new FunctionCall(call.getName(), args, call.getPosition());

      FunctionResolver resolver = FunctionResolverFactory.getResolver(call);

      if (matchedFuncHolder instanceof DrillComplexWriterFuncHolder && ! allowComplexWriter) {

        errorCollector.addGeneralError(call.getPosition(), "Only ProjectRecordBatch could have complex writer function. You are using complex writer function " + call.getName() + " in a non-project operation!");

      }

      //new arg lists, possible with implicit cast inserted.

      List<LogicalExpression> argsWithCast = Lists.newArrayList();

      if (matchedFuncHolder!=null) {

        //Compare parm type against arg type. Insert cast on top of arg, whenever necessary.

        for (int i = 0; i < call.args.size(); ++i) {

          LogicalExpression currentArg = call.args.get(i);

          //Case 1: If  1) the argument is NullExpression

          //            2) the parameter of matchedFuncHolder allows null input, or func's null_handling is NULL_IF_NULL (means null and non-null are exchangable).

          //        then replace NullExpression with a TypedNullConstant

          if (currentArg.equals(NullExpression.INSTANCE) &&

            ( parmType.getMode().equals(TypeProtos.DataMode.OPTIONAL) ||

            argsWithCast.add(new TypedNullConstant(parmType));

            //Case 2: argument and parameter matches, or parameter is FieldReader.  Do nothing.

            argsWithCast.add(currentArg);

          } else {

            //Case 3: insert cast if param type is different from arg type.

            argsWithCast.add(addCastExpression(call.args.get(i), parmType, registry));

          }

        }

      }

      // as no drill func is found, search for a non-Drill function.

      AbstractFuncHolder matchedNonDrillFuncHolder = registry.findNonDrillFunction(call);

      if (matchedNonDrillFuncHolder != null) {

      String funcName = "convertToNullable" + minorType.toString();

      FunctionCall funcCall = new FunctionCall(funcName, args, ExpressionPosition.UNKNOWN);

      FunctionResolver resolver = FunctionResolverFactory.getResolver(funcCall);

      if (matchedConvertToNullableFuncHolder == null) {

        logFunctionResolutionError(errorCollector, funcCall);

        return NullExpression.INSTANCE;

      }

    }