I'm using jira rest client api 5.1.0, but due to GDPR change I have a problem with search user

[Mia Simundic]

I'm using jira rest client api 5.1.0, but due to GDPR change I have a problem with search user.

What is substitution for this: 

Promise<Iterable<User>> findUsers(String username, @Nullable Integer startAt, @Nullable Integer maxResults,
        @Nullable Boolean includeActive, @Nullable Boolean includeInactive); 


GET path/search?searchTerm=mar

Response: 

{    "statusCode": "ERROR",   
 "message": "java.util.concurrent.ExecutionException: com.google.api.client.http.HttpResponseException: 400\n{\"errorMessages\":[\"The query parameter 'username' is not supported in GDPR strict mode.\"],\"errors\":{}
}"

How can I search for users now to fill assignee field?

Thanx in advance!