Remove required state of description

lib/api/v3/work_packages/schema/work_package_schema_representer.rb

@@ -120,7 +120,8 @@ module API
                  max_length: 255
 
           schema :description,
-                 type: 'Formattable'
+                 type: 'Formattable',
+                 required: false
 
           schema :start_date,
                  type: 'Date',

spec/features/work_packages/details/inplace_editor/description_editor_spec.rb

@@ -40,7 +40,8 @@ describe 'description inplace editor', js: true, selenium: true do
       field.expect_state_text 'Click to enter description...'
 
       field.activate!
-      field.expect_save_button(enabled: false)
+      # An empty description is also allowed
+      field.expect_save_button(enabled: true)
       field.set_value 'A new hope ...'
       field.expect_save_button(enabled: true)
       field.submit_by_click

spec/lib/api/v3/work_packages/schema/work_package_schema_representer_spec.rb

@@ -175,7 +175,7 @@ describe ::API::V3::WorkPackages::Schema::WorkPackageSchemaRepresenter do
         let(:path) { 'description' }
         let(:type) { 'Formattable' }
         let(:name) { I18n.t('attributes.description') }
-        let(:required) { true }
+        let(:required) { false }
         let(:writable) { true }
       end
     end