split up the nil? and empty? cases, because they are different

situations

app.rb

@@ -50,9 +50,14 @@ class App < Roda
         end
 
         url = r.params['url']
-        if url.nil? or url.empty? 
+        if url.nil?
           response.status = 400
-          return {message: "Please enter a valid URL"}
+          return {message: "missing url parameter"}.to_json
+        end
+
+        if url.empty? 
+          response.status = 400
+          return {message: "invalid url parameter"}.to_json
         end
 
         if links.filter(:url => url).first.nil?

spec/create_spec.rb

@@ -25,7 +25,7 @@ describe "Submit API request to create new link" do
   after :each do
     @links.delete
   end
-  it "should return link data in json format when a valid url is entered" do
+  it "should return link data in json format when a valid url is submitted" do
     data = {
       url: 'http://google.com'
     }
@@ -36,5 +36,25 @@ describe "Submit API request to create new link" do
     expect(response_json['code']).not_to eq(nil)
     expect(response_json['link']).to include(response_json['code'])
   end
+  
+  it "should return with a 400 status and 'invalid url parameter' message when an empty url is submitted" do
+    data = {
+      url: ''
+    }
+    post('/links', data.to_json, "CONTENT_TYPE" => "application/json")
+    expect(last_response.status).to eq(400)
+    response_json = JSON.parse(last_response.body)
+    expect(response_json['message']).to eq('invalid url parameter')
+
+  end
+  it "should return with a 400 status and 'missing url parameter' message when an empty url is submitted" do
+    data = {
+    }
+    post('/links', data.to_json, "CONTENT_TYPE" => "application/json")
+    expect(last_response.status).to eq(400)
+    response_json = JSON.parse(last_response.body)
+    expect(response_json['message']).to eq('missing url parameter')
+
+  end
 end