Error in formula or condition: '>' not supported between instances of 'NoneType' and 'int'

hello i am facing this issue when i hahev given follwing condition in salary structure and generating pay slip condition is:- base >1500 and formula is base * 0.4. but it is giveing error.

in salary structure assignment doctype the Base field is not proper i think.

can anyone please provide me the salary structure assignment base details.

Urgently required.

Please check if base field has some value and is not blank on whichever event the code is triggered.

Yes the base is filled during salary assignment and it is filled at that time.