How can I get all current custom fields in a project?

[Abdulrahman Riaz]

I am currently working on a task where I need to import some data to jira but I need to map it to custom fields 

So I need to first check if those fields exist if they don't I want to create them and assign them the data.

[Abdulrahman Riaz]

/rest/api/3/field?maxResults=150
I can get all fields with this api but is it possible to search for fields and it would return results if they exist? 

like 

/rest/api/3/field?maxResults=150&asset exists? & threatId exits? &...