I'm using a paging grid to add the data to the same on clink of a button aft

What expression are you using for your null check? Try using rule!APN_isBlank() from Appian Common Objects

Assuming you are using different data at runtime than in the interface designer, it looks like you might be trying to create a grid without any data, which could cause problems if your null checks are for individual elements. If that is the case, you could wrap the whole grid in a null check, something like:
if ( isnull( <grid data>, a!textField(label: "There is no data to display"), <your grid here> )

From the error message it looks like one of the value in identifiers array is null. To find and remove the null value from array, use this expression by passing identifier array as input. - remove(ri!input, where(apply(isnull(_), ri!input))) -

After doing this you might get another error saying that the number of values in every column must be same. This is because we have removed null values from identifiers array and left other column as is. After getting the index of null values try to remove the row from gridData CDT. Ideally we shouldn't get null values in identifiers array as it is often same as primary value.

Thanks, I have sorted out the issues, as there is a difference set function which was filtering null values on the cdt comparison.. Thanks Everyone for the support.