Trim possible attribute values like attribute values setup by a user (#1044)

cvat-ui/src/components/labels-editor/label-form.tsx

@@ -67,6 +67,8 @@ class LabelForm extends React.PureComponent<Props, {}> {
                             }
                         }
 
+                        attrValues = attrValues.map((value: string) => value.trim());
+
                         return {
                             name: formValues.attrName[key],
                             type: formValues.type[key],

cvat/apps/engine/serializers.py

@@ -22,7 +22,7 @@ class AttributeSerializer(serializers.ModelSerializer):
     # pylint: disable=no-self-use
     def to_internal_value(self, data):
         attribute = data.copy()
-        attribute['values'] = '\n'.join(data.get('values', []))
+        attribute['values'] = '\n'.join(map(lambda x: x.strip(), data.get('values', [])))
         return attribute
 
     def to_representation(self, instance):