Error 201 on TSimpleMsgPack.setAsString if string is empty

[cpicanco]

    procedure TSimpleMsgPack.setAsString(pvValue: string);
    begin
      FDataType := mptString;
      if SizeOf(Char) = 2 then
      begin
        SetLength(FValue, length(pvValue) shl 1);
        Move(PChar(pvValue)^, FValue[0], Length(FValue));
      end else
      begin
        SetLength(FValue, length(pvValue));
        Move(PChar(pvValue)^, FValue[0], Length(FValue)); // <<<<<<<<< error Runtime (201)
      end;
    end;

Any suggestion will be appreciated.

Docs for me:
http://wiki.freepascal.org/Character_and_string_types
http://www.freepascal.org/docs-html/rtl/system/stringfunctions.html
http://www.freepascal.org/docs-html/ref/refsu10.html

[ymofen]

error Runtime
what's error message?

[cpicanco]

When length(pvValue) = 0

http://www.freepascal.org/docs-html/user/userap4.html
201 Range check error

If you compiled your program with range checking on, then you can get this error in the following cases:

• An array was accessed with an index outside its declared range.
• Trying to assign a value to a variable outside its range (for instance an enumerated type).