def getHelmSvc(Map helmSvc,String mservice){
                def domain = helmSvc[mservice].domain
                def microservice_name = helmSvc[mservice].microservice_name
                def ingress_required = helmSvc[mservice].ingress_required
                def var_map = [:]
                var_map['microservice_name'] = microservice_name
                var_map['ingress_required'] = ingress_required
                return var_map

        }

text1=new File('/jenkins/workspace/helm/helm_svc.yml').text

                    Yaml yaml = new Yaml()
                    def obj = yaml.load(text1)

                    ret=getHelmSvc(obj, mservice)
                    println ret

Basically it's printing on console:
          {microservice_name=some-processor, ingress_required=false}

sh("""
                      echo "$ret" >  "/jenkins/workspace/helm/map.yml"
          """)

an exception which occurred:
in field com.cloudbees.groovy.cps.impl.BlockScopeEnv.locals
in object com.cloudbees.groovy.cps.impl.BlockScopeEnv@2b3f4d48
in field com.cloudbees.groovy.cps.impl.CallEnv.caller
in object com.cloudbees.groovy.cps.impl.FunctionCallEnv@2ee0ffec
in field com.cloudbees.groovy.cps.Continuable.e
in object org.jenkinsci.plugins.workflow.cps.SandboxContinuable@108a4042
in field org.jenkinsci.plugins.workflow.cps.CpsThread.program
in object org.jenkinsci.plugins.workflow.cps.CpsThread@28b2f39d
in field org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.threads
in object org.jenkinsci.plugins.workflow.cps.CpsThreadGroup@1a7da7eb
in object org.jenkinsci.plugins.workflow.cps.CpsThreadGroup@1a7da7eb
        Caused: java.io.NotSerializableException: org.yaml.snakeyaml.Yaml