Why does a NULL value appear when I count to create a lead and validate duplicates?

[#1]

Hi!

I am generating a key by concatenating the fields and with the image script valid in impala that they are not duplicated, apparently there are no duplicates but I get NULL and this number is 148724. That is not true. There are no duplicates and there should be 0 records.

Thank you!

[#2]

To pinpoint the root cause, kindly provide a few samples of data