Fix NPE in bigquery XXXInfo.equals

gcloud-java-bigquery/src/main/java/com/google/gcloud/bigquery/DatasetInfo.java

@@ -396,7 +396,8 @@ public int hashCode() {
 
   @Override
   public boolean equals(Object obj) {
-    return obj.getClass().equals(DatasetInfo.class)
+    return obj != null
+        && obj.getClass().equals(DatasetInfo.class)
         && Objects.equals(toPb(), ((DatasetInfo) obj).toPb());
   }
 

gcloud-java-bigquery/src/main/java/com/google/gcloud/bigquery/JobInfo.java

@@ -319,7 +319,9 @@ public int hashCode() {
 
   @Override
   public boolean equals(Object obj) {
-    return obj.getClass().equals(JobInfo.class) && Objects.equals(toPb(), ((JobInfo) obj).toPb());
+    return obj != null
+        && obj.getClass().equals(JobInfo.class)
+        && Objects.equals(toPb(), ((JobInfo) obj).toPb());
   }
 
   JobInfo setProjectId(String projectId) {

gcloud-java-bigquery/src/main/java/com/google/gcloud/bigquery/TableInfo.java

@@ -339,7 +339,8 @@ public int hashCode() {
 
   @Override
   public boolean equals(Object obj) {
-    return obj.getClass().equals(TableInfo.class)
+    return obj != null
+        && obj.getClass().equals(TableInfo.class)
         && Objects.equals(toPb(), ((TableInfo) obj).toPb());
   }