fix(github_hooks): return null if commit author is nil (#195)

Author: forestileao

github_hooks/lib/repo_host/bitbucket/payload.rb

@@ -97,9 +97,7 @@ def head_commit_message
 
     # ✔️
     def commit_author
-      if @commits.present? && @commits.last.present?
-        @commits.last["author"]["user"]["nickname"]
-      end
+      @commits.last&.dig("author", "user", "nickname") || ""
     end
 
     # ✔️

github_hooks/spec/lib/repo_host/bitbucket/payload_spec.rb

@@ -115,6 +115,9 @@ def build_payload(string)
         expect(payload_for_branch_deletion.author_email).to eq ""
         expect(payload_for_new_branch_with_new_commits.author_email).to eq ""
         expect(payload_for_new_branch_without_new_commits.author_email).to eq ""
+        expect(payload_for_branch_deletion.commit_author).to eq ""
+        expect(payload_for_new_branch_with_new_commits.commit_author).to eq "milana_stojadinov"
+        expect(payload_for_new_branch_without_new_commits.commit_author).to eq "milana_stojadinov"
       end
     end