Merge pull request #1924 from saparaj/release-13

CherryPick:13 Guard against NPE in manageRelationFromResourceToSubResources from Discovery class

Author: brendandburns

util/src/main/java/io/kubernetes/client/Discovery.java

@@ -116,7 +116,11 @@ private Map<String, Set<String>> manageRelationFromResourceToSubResources(
               getSubResourceNameIfPossible(r.getName())
                   .ifPresent(
                       subResourceName -> {
-                        subResources.get(getMajorResourceName(r.getName())).add(subResourceName);
+                        subResources
+                            .computeIfAbsent(
+                                getMajorResourceName(r.getName()),
+                                majorResourceName -> new HashSet<>())
+                            .add(subResourceName);
                       });
             });
     return subResources;