check if its value is not defined

VarIsEmptyOrNull.pas

function VarIsEmptyOrNull(const Value: Variant): Boolean;
begin
  Result := VarIsClear(Value)
         or VarIsEmpty(Value)
         or VarIsNull(Value)
         or (VarCompareValue(Value, Unassigned) = vrEqual);
  
  if (not Result) and VarIsStr(Value) then
     Result := Value = EmptyStr;
end;