pushes/harmony: use to_s.strip.empty? to check if app is set

plugins/pushes/harmony/config.rb

@@ -72,7 +72,7 @@ module VagrantPlugins
       def validate(machine)
         errors = _detected_errors
 
-        if @app == nil || @app == ""
+        if @app.to_s.strip.empty?
           errors << I18n.t("push_harmony.errors.config.app_required")
         end
 

test/unit/plugins/pushes/harmony/config_test.rb

@@ -50,6 +50,12 @@ describe VagrantPlugins::HarmonyPush::Config do
       assert_invalid
     end
 
+    it "is invalid if blank" do
+      subject.app = "   "
+      subject.finalize!
+      assert_invalid
+    end
+
     it "is valid if set" do
       subject.app = "foo/bar"
       subject.finalize!