Tidy up potential NPEs from github comments

Author: tarnfeld

src/main/java/org/apache/mesos/hadoop/Utils.java

@@ -11,6 +11,7 @@
 
 import org.apache.mesos.Protos.CommandInfo;
 import org.apache.mesos.Protos.ContainerInfo;
+import org.apache.mesos.Protos.ContainerInfo.DockerInfo;
 import org.apache.mesos.Protos.Parameter;
 import org.apache.mesos.Protos.Parameters;
 import org.apache.mesos.Protos.Volume;
@@ -63,25 +64,25 @@ public static CommandInfo.ContainerInfo buildContainerInfo(Configuration conf) {
 
   public static ContainerInfo buildDockerContainerInfo(Configuration conf) {
     ContainerInfo.Builder containerInfoBuilder = ContainerInfo.newBuilder();
-    ContainerInfo.DockerInfo.Builder dockerInfoBuilder = ContainerInfo.DockerInfo.newBuilder();
+    DockerInfo.Builder dockerInfoBuilder = DockerInfo.newBuilder();
 
     dockerInfoBuilder.setImage(conf.get("mapred.mesos.docker.image"));
 
     switch (conf.getInt("mapred.mesos.docker.network", 1)) {
       case 1:
-        dockerInfoBuilder.setNetwork(ContainerInfo.DockerInfo.Network.HOST);
+        dockerInfoBuilder.setNetwork(DockerInfo.Network.HOST);
       case 2:
-        dockerInfoBuilder.setNetwork(ContainerInfo.DockerInfo.Network.BRIDGE);
+        dockerInfoBuilder.setNetwork(DockerInfo.Network.BRIDGE);
       case 3:
-        dockerInfoBuilder.setNetwork(ContainerInfo.DockerInfo.Network.NONE);
+        dockerInfoBuilder.setNetwork(DockerInfo.Network.NONE);
     }
 
     dockerInfoBuilder.setPrivileged(conf.getBoolean("mapred.mesos.docker.privileged", false));
     dockerInfoBuilder.setForcePullImage(conf.getBoolean("mapred.mesos.docker.force_pull_image", false));
 
     // Parse out any additional docker CLI params
     String[] params = conf.getStrings("mapred.mesos.docker.parameters");
-    if (params.length > 0) {
+    if (params != null && params.length > 0) {
       assert (params.length % 2) == 0; // Make sure we have an even number of parameters
 
       Parameter.Builder paramBuilder = null;
@@ -99,7 +100,7 @@ public static ContainerInfo buildDockerContainerInfo(Configuration conf) {
 
     // Parse out any volumes that have been defined
     String[] volumes = conf.getStrings("mapred.mesos.docker.volumes");
-    if (volumes.length > 0) {
+    if (volumes != null && volumes.length > 0) {
       for (int i = 0; i < volumes.length; i++) {
         String[] parts = volumes[i].split(":");
         assert parts.length > 1;