Fix N/A search for Schedule-a and Schedule-b

[fec-jli]

What we’re after

When we search for contributor_occupation and contributor_employer on all receipts page, filter by 'N/A',
return a lot of wrong result that most of contributor_occupation value are not equal 'N/A'

When we search for disbursement_description on all disbursements page, filter by 'N/A',
return a lot of wrong result that most of disbursement_description value are not equal 'N/A'

Ex1: contributor_occupation=N/A, return about 2,805,000 rows for '/schedules/schedule_a/'
https://www.fec.gov/data/receipts/?data_type=processed&contributor_occupation=N%2FA&two_year_transaction_period=2024&min_date=01%2F01%2F2023&max_date=12%2F31%2F2024

Ex2: contributor_employer=N/A, return about 1,534,000 rows for '/schedules/schedule_a/'
https://www.fec.gov/data/receipts/?data_type=processed&contributor_employer=N%2FA&two_year_transaction_period=2024&min_date=01%2F01%2F2023&max_date=12%2F31%2F2024

Ex3: disbursement_description=N/A, return about 50,781 rows for '/schedules/schedule_b/'
https://www.fec.gov/data/disbursements/?data_type=processed&two_year_transaction_period=2024&min_date=01%2F01%2F2023&max_date=12%2F31%2F2024&disbursement_description=N%2FA

This PR will fix filter by 'N/A' for '/schedules/schedule_a/' and '/schedules/schedule_b/' endpoints.

Related cms ticket(s)

fecgov/fec-cms#5220

Action item(s)

• Fix filter by 'N/A/', return correct result

References

PR: #5809