To retrieve data from JIRA REST API call, field is empty/none, it throws null pointer exception

[younoos]

While trying to query JIRA using REST API call using following query, 

https://jira-home.com/rest/api/latest/search?jql=issuetype=Risk%20AND%20project%20in%20("CJI","PPM","CGCPM","RL")&fields=key,project,summary,description,customfield_11900,customfield_11903,customfield_11904,customfield_15700,customfield_11905,customfield_11906,customfield_13903,customfield_11901,issuetype,status,customfield_15500,customfield_11902,duedate,assignee&maxResults=1000

it throws "Null Pointer Exception" when some of the non-mandatory custom fields are empty / none value.

Please help in fixing this issue.