DEV: Improve ArgumenError raised in PostOwnerChanger. (#15907)

Currently, it doesn't provide any context about the arguement which
caused the error.

app/services/post_owner_changer.rb

@@ -9,7 +9,9 @@ class PostOwnerChanger
     @acting_user = params[:acting_user]
     @skip_revision = params[:skip_revision] || false
 
-    raise ArgumentError unless @post_ids && @topic && @new_owner && @acting_user
+    [:post_ids, :topic, :new_owner, :acting_user].each do |arg|
+      raise ArgumentError.new(arg) if self.instance_variable_get("@#{arg}").blank?
+    end
   end
 
   def change_owner!

spec/services/post_owner_changer_spec.rb

@@ -14,7 +14,7 @@ describe PostOwnerChanger do
     it "raises an error with a parameter missing" do
       expect {
         PostOwnerChanger.new(post_ids: [p1.id], topic_id: topic.id, new_owner: nil, acting_user: editor)
-      }.to raise_error(ArgumentError)
+      }.to raise_error(ArgumentError, /new_owner/)
     end
 
     it "calls PostRevisor" do