Don't reset the value if a new value is provided

If a value is provided with a request to update the record, we should
not nullify it. We don't send decrypted private values to the client, so
if client provides it, it's probably pasted by the user.

lib/travis/api/app/endpoint/env_vars.rb

@@ -13,7 +13,7 @@ class Travis::Api::App
         record.update(data)
 
         # if we update from private to public reset value
-        if !previously_public && record.public?
+        if !previously_public && record.public? && data['value'].nil?
           record.value = nil
         end
 

spec/integration/v2/settings/env_vars_spec.rb

@@ -83,6 +83,20 @@ describe Travis::Api::App::SettingsEndpoint do
     end
 
     describe 'PATCH /settings/env_vars/:id' do
+      it 'resets value if private key is made public unless new value is provided' do
+        settings = repo.settings
+        env_var = settings.env_vars.create(name: 'FOO', value: 'bar')
+        settings.save
+
+        body = { env_var: { public: true, value: 'a new value' } }.to_json
+        response = patch "/settings/env_vars/#{env_var.id}?repository_id=#{repo.id}", body, headers
+        json = JSON.parse(response.body)
+        json['env_var']['value'].should == 'a new value'
+
+        updated_env_var = repo.reload.settings.env_vars.find(env_var.id)
+        updated_env_var.value.decrypt.should == 'a new value'
+      end
+
       it 'resets value if private key is made public' do
         settings = repo.settings
         env_var = settings.env_vars.create(name: 'FOO', value: 'bar')