Capturing and displaying user input in Crystal Reports

Hi all,

Iu2019m creating a crystal report with SAP as data-source and want to capture user input and display it on the report. I have defined parameters to capture the input and added them to the report header. I have then created formula fields to capture user input using the JOIN statement to accommodate multiple values. Everything works well when users enter values for all the parameters, but when they leave some blank I get an error message u201CParameter value is nullu201D.

Has anyone encountered this type of problem; Anyone knows how to resolve this?