Error query script generation failed no member found for caption filter

Hello,

I create a webi document on a Bex query, to permit users to enter manually Material key in this document, I create a filter in webi document as a prompt, so users can enter lot of material key manually.

My problem is if a user enter a key that doesn't exist in the Cube BW i have an error:

Query script generation failed, no member found for caption filter...

But if the material key doesn't exit i just want to have the result of the webi document with non data

Emilie