@chandramohan27 Can you share the workflow? Depending on how you are using the loop, that could be causing the issue. If you have steps after the loop aside from an End Step, they may not function as you intended.
@iamnithesh is correct with Verifying the data type is not blank first. I ran into this issue with a Define Variable as documented here: Workflow - Define Variable: Blank/missing value outputs the JSON variable path
The current workaround for that is to check if it is null, then handle that case separately.