Added GHBranch creator

Added GHBranch creator and added a test to make sure it works

src/main/java/org/kohsuke/github/GHBranch.java

@@ -1,8 +1,8 @@
 package org.kohsuke.github;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
-
 import java.io.IOException;
 import java.net.URL;
 import java.util.Collection;
@@ -26,7 +26,15 @@ public class GHBranch {
     private boolean protection;
     private String protection_url;
 
-
+    @JsonCreator
+    GHBranch(@JsonProperty("name") String name) throws Exception{
+        if (name != null) {
+            this.name = name;
+        }
+        else{
+            throw new GHFileNotFoundException("Branch Not Found");
+        }
+    }
     public static class Commit {
         String sha;
 

src/test/java/org/kohsuke/github/GHRepositoryTest.java

@@ -60,8 +60,9 @@ public void getBranchNonExistentBut200Status() throws Exception {
             GHBranch branch = repo.getBranch("test/NonExistent");
             fail();
         }
-        catch(GHFileNotFoundException e){
-            assertEquals("{\"message\":\"Branch not found\",\"documentation_url\":\"https://developer.github.com/v3/repos/branches/#get-branch\"}", e.getMessage());
+        catch(Exception e){
+            //I dont really love this but I wanted to get to the root wrapped cause
+            assertEquals("Branch Not Found", e.getCause().getCause().getCause().getMessage());
         }
     }