public override void Validate(
     ExprNodeOrigin origin,
     ExprValidationContext validationContext)
 {
     Rhs = GetValidatedSubtree(origin, Rhs, validationContext);
     Lhs.Validate(origin, validationContext);
     EPStatementStartMethodHelperValidate.ValidateNoAggregations(Rhs, ValidationAggMsg);
 }