fix npe

apollo-adminservice/src/main/java/com/ctrip/framework/apollo/adminservice/controller/ReleaseHistoryController.java

@@ -122,7 +122,7 @@ public class ReleaseHistoryController {
         releaseHistories.add(releaseHistory);
 
         //rollback
-        if (release.isAbandoned()) {
+        if (release.isAbandoned() && previousRelease != null) {
           releaseHistory.setDataChangeLastModifiedTime(release.getDataChangeCreatedTime());
           ReleaseHistory rollBackReleaseHistory = assembleReleaseHistory(previousRelease,
               ReleaseOperation.ROLLBACK, release.getId());

apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/ReleaseService.java

@@ -220,11 +220,12 @@ public class ReleaseService {
     Map<String, String> parentConfigurations = parentLatestRelease != null ?
                                                gson.fromJson(parentLatestRelease.getConfigurations(),
                                                              configurationTypeReference) : new HashMap<>();
+    long baseReleaseId = parentLatestRelease == null ? 0 : parentLatestRelease.getId();
 
     Map<String, String> childNamespaceToPublishConfigs = mergeConfiguration(parentConfigurations, childNamespaceItems);
     Release release =
         branchRelease(parentNamespace, childNamespace, releaseName, releaseComment,
-                      childNamespaceToPublishConfigs, parentLatestRelease.getId(), operator,
+                      childNamespaceToPublishConfigs, baseReleaseId, operator,
                       ReleaseOperation.GRAY_RELEASE);
 
     return release;