Mods to fix cast class exception related to jira_issue_transition_id (#253).

src/main/java/org/gitlab4j/api/services/JiraService.java

 package org.gitlab4j.api.services;
 
+import java.util.Map;
+
 import javax.xml.bind.annotation.XmlAccessType;
 import javax.xml.bind.annotation.XmlAccessorType;
 import javax.xml.bind.annotation.XmlRootElement;
@@ -109,4 +111,28 @@ public class JiraService extends NotificationService {
         setJiraIssueTransitionId(jiraIssueTransitionId);
         return (this);
     }
+
+    @Override
+    public void setProperties(Map<String, Object> properties) {
+        fixJiraIssueTransitionId(properties);
+        super.setProperties(properties);
+    }
+
+    /**
+     * Make sure jiraIssueTransitionId is an integer and not an empty string.
+     * @param properties the Map holding the properties
+     */
+    private void fixJiraIssueTransitionId(Map<String, Object> properties) {
+
+        if (properties != null) {
+            Object jiraIssueTransitionId = properties.get(JIRA_ISSUE_TRANSITION_ID_PROP);
+            if (jiraIssueTransitionId instanceof String) {
+                if (((String)jiraIssueTransitionId).trim().isEmpty()) {
+                    properties.put(JIRA_ISSUE_TRANSITION_ID_PROP, null);
+                } else {
+                    properties.put(JIRA_ISSUE_TRANSITION_ID_PROP, Integer.valueOf((String)jiraIssueTransitionId));
+                }
+            }
+        }
+    }
 }

src/test/java/org/gitlab4j/api/TestServicesApi.java

@@ -105,8 +105,14 @@ public class TestServicesApi {
 
     @Test
     public void testGetJiraService() throws GitLabApiException {
+
         JiraService jiraService =  gitLabApi.getServicesApi().getJiraService(testProject);
         assertNotNull(jiraService);
+
+        // Make sure the jira_issue_transition_id is retrievable.
+        // This is testing that a class cast exception is not thrown.
+        Integer jiraIssueTransitionId = jiraService.getJiraIssueTransitionId();
+        assertTrue(jiraIssueTransitionId == null || jiraIssueTransitionId != null);
     }
 
     @Test