Hi Harshita,
It appears that your source is a NUMC type field (ony numbers in a character field, used mostly for document numbers) . "0" or "0000" for NUMC 4 field is the null.
Your screen shot indicates that you have store a Null value.
You should be able to select "0000" for a NUMC 4.
If not, then "#" through BEX
If not, try using , < 1 as selection criteria.
Also consider using "Maintain Master Data" to add "Null" to english text, and search for "Null" in the text.
Let me know if this helped,
John Hawk