Make MongoDB database stats and CPU (hostInfo) optional

Refs Graylog2/graylog2-server#1195

Author: Jochen Schalanda

src/main/java/org/graylog/plugins/usagestatistics/collectors/MongoCollector.java

@@ -35,24 +35,29 @@ public MongoCollector(ClusterStatsService clusterStatsService) {
     public MongoStats getMongoStats() {
         final org.graylog2.system.stats.mongo.MongoStats stats = clusterStatsService.mongoStats();
         final DatabaseStats databaseStats = stats.databaseStats();
-        final MongoDatabaseStats mongoDatabaseStats = MongoDatabaseStats.create(
-                databaseStats.collections(),
-                databaseStats.objects(),
-                databaseStats.avgObjSize(),
-                databaseStats.dataSize(),
-                databaseStats.storageSize(),
-                databaseStats.numExtents(),
-                databaseStats.indexes(),
-                databaseStats.indexSize(),
-                databaseStats.fileSize(),
-                databaseStats.nsSizeMB()
-        );
 
+        final MongoDatabaseStats mongoDatabaseStats;
+        if (databaseStats != null) {
+            mongoDatabaseStats = MongoDatabaseStats.create(
+                    databaseStats.collections(),
+                    databaseStats.objects(),
+                    databaseStats.avgObjSize(),
+                    databaseStats.dataSize(),
+                    databaseStats.storageSize(),
+                    databaseStats.numExtents(),
+                    databaseStats.indexes(),
+                    databaseStats.indexSize(),
+                    databaseStats.fileSize(),
+                    databaseStats.nsSizeMB()
+            );
+        } else {
+            mongoDatabaseStats = null;
+        }
 
         return MongoStats.create(
                 stats.buildInfo().version(),
                 stats.servers().size(),
-                stats.hostInfo().system().cpuArch(),
+                stats.hostInfo() == null ? "unknown" : stats.hostInfo().system().cpuArch(),
                 mongoDatabaseStats
         );
     }

src/main/java/org/graylog/plugins/usagestatistics/dto/MongoStats.java

@@ -19,10 +19,13 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.auto.value.AutoValue;
 
+import javax.annotation.Nullable;
+
 @JsonAutoDetect
 @AutoValue
 public abstract class MongoStats {
-    public static MongoStats create(String version, int serverCount, String cpuArch, MongoDatabaseStats databaseStats) {
+    public static MongoStats create(String version, int serverCount, String cpuArch,
+                                    @Nullable MongoDatabaseStats databaseStats) {
         return new AutoValue_MongoStats(version, serverCount, cpuArch, databaseStats);
     }
 
@@ -36,5 +39,6 @@ public static MongoStats create(String version, int serverCount, String cpuArch,
     public abstract String cpuArch();
 
     @JsonProperty
+    @Nullable
     public abstract MongoDatabaseStats databaseStats();
 }