Calculate Custom Fields values in Scripted Field using Scriptrunner in JIRA Cloud

Hi Community, 

In Jira Cloud, I have two custom fields: Compliance and Audit (Select List - single choice).

I have created two Text Fields (single line): Risk Score and Risk Level which will be used as Scripted Field in Scriptrunner in Jira Cloud.

First, I am writing this below code to calculate the sum of Compliance and Audit and show the result in Risk Score:

def complianceField = "customfield_XXXXX" //Compliance
def auditField = "customfield_YYYYY" //Audit
def result = get("/rest/api/2/issue/${issue.key}")
             .queryString("fields", "customfield_10280,customfield_10281")
             .header('Content-Type', 'application/json')
             .asObject(Map)

String complianceFieldValue = result.body.fields[complianceField]?.value
String auditFieldValue = result.body.fields[auditFieldValue]?.value

def retval = 0
switch (complianceFieldValue) {
              case ('Impacts from 10 and above'):
                             retval+=9;
                             break;
              case ('Impacts from 5 to 10'):
                             retval+=5;
                             break;
              case ('Impacts from 3 to 5'):
                             retval+=3;
                             break;
              default:
                             retval+=0;
                             break;
}
switch (auditFieldValue) {
              case ('Impacts more than 1000 consumers'):
                             retval+=9;
                             break;
              case ('Impacts between 500 consumers'):
                             retval+=5;
                             break;
              case ('Impacts less than 300 consumers'):
                             retval+=3;
                             break;
              default:
                             retval+=0;
                             break;
}
return retval.toString();

But facing Static type checking error in the above code. Please guide further in resolving the issue.