import com.atlassian.jira.ComponentManager
import com.atlassian.jira.issue.fields.CustomField
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.label.LabelManager
import org.springframework.util.StringUtils
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

labelManager = ComponentManager.getComponentInstanceOfType(LabelManager.class)
CustomFieldManager customFieldManager = ComponentManager.getInstance().getCustomFieldManager();


CustomField UseCustomer = customFieldManager.getCustomFieldObject(10600);
CustomField Customer = customFieldManager.getCustomFieldObject(10900);


labelManager.removeLabelsForCustomField(10900)


//Remove all labels
labelManager.removeLabelsForCustomField(10900)
 Set labelSet = new HashSet();
labelSet.add(issue.getCustomFieldValue(UseCustomer));


def componentManager = ComponentManager.getInstance()
def authContext = componentManager.getJiraAuthenticationContext()
def user = authContext.getUser()


//Set new label issue.getCustomFieldValue(UseCustomer)
labelManager.setLabels(user, issue.id,<set>labelSet, false,false)