Having trouble with challenge.

Goal is to add a new method called getCategoryCounts. It should return a Map of category to count calculated by looping over all the posts. My error is Bummer! For category Entertainment, expected 1 but received null. I think the problem may be in the nested for each loops but I don't know how to debug/test on this platform. Thanks.

My code:

public class Blog { List<BlogPost> mPosts;

public String Key; public int count;

public Blog(List<BlogPost> posts) { mPosts = posts; }

public List<BlogPost> getPosts() { return mPosts; }

public Set<String> getAllAuthors() { Set<String> authors = new TreeSet<>(); for (BlogPost post: mPosts) { authors.add(post.getAuthor()); } return authors; } Set <String> categories = new HashSet<String>(); //Get unique set of categories public Set<String> getAllCategories() {

 for (BlogPost post: mPosts) {
  categories.add(post.getCategory());
    }
   return categories;  
   }
  public Map<String, Integer> getCategoryCounts() {
 // Converting categories Set to Array
String[] arrayString = categories.toArray(new String[categories.size()]);
Map<String, Integer> categoryCounts = new HashMap<String, Integer>();
for (String Key : arrayString) {
      count = 0;
    for (BlogPost post: mPosts) {
      if (Key == post.getCategory())
        count++;
        categoryCounts.put(Key,count);
      }
    }    
     return categoryCounts;
  }

}

package com.example;

import java.io.Serializable; import java.util.ArrayList; import java.util.Date; import java.util.List;

public class BlogPost implements Comparable<BlogPost>, Serializable { private String mAuthor; private String mTitle; private String mBody; private String mCategory; private Date mCreationDate;

public BlogPost(String author, String title, String body, String category, Date creationDate) { mAuthor = author; mTitle = title; mBody = body; mCategory = category; mCreationDate = creationDate; }

public int compareTo(BlogPost other) { if (equals(other)) { return 0; } return mCreationDate.compareTo(other.mCreationDate); }

public String[] getWords() { return mBody.split("\s+"); }

public List<String> getExternalLinks() { List<String> links = new ArrayList<String>(); for (String word : getWords()) { if (word.startsWith("http")) { links.add(word); } } return links; }

public String getAuthor() { return mAuthor; }

public String getTitle() { return mTitle; }

public String getBody() { return mBody; }

public String getCategory() { return mCategory; }

public Date getCreationDate() { return mCreationDate; } }