I have some SQL like this:

SELECT * FROM
MY_STORED_PROC(:INT_PARAM1, :STRING_PARAM, :INT_PARAM2)

It executes correctly and returns the data I want, however, when I
move to the last record (or Delphi moves there in an attempt to
populate a grid) I get this error:

Overflow occured during data type conversion
Conversion error from string "".

What's would cause this? How can I prevent it?