As JQL is not case sensitive (https://confluence.atlassian.com/jiracoreserver/search-syntax-for-text-fields-939937723.html), when having multiple custom fields with the same name and different case (e.g. numberfield and numberField) using the JQL below does not correctly filter based on the desired field content:

numberfield is empty

However if we use the custom field ID it does retrieve the data properly:

cf[10202] is empty

As a quality of life improvement, we could add case sensitivity to the queries, which would allow customers to search based on field names only.