models2: Fixed StoryCategory UnmarshalGQL validating before writing the value.

models/story-category.go

@@ -1,6 +1,7 @@
 package models
 
 import (
+	"errors"
 	"fmt"
 	"io"
 )
@@ -35,14 +36,13 @@ func (e *StoryCategory) IsValid() bool {
 func (e *StoryCategory) UnmarshalGQL(v interface{}) error {
 	str, ok := v.(string)
 	if !ok {
-		return fmt.Errorf("enums must be strings")
-	}
-
-	if !e.IsValid() {
-		return fmt.Errorf("%s is not a valid StoryCategory", str)
+		return errors.New("enums must be strings")
 	}
 
 	*e = StoryCategory(str)
+	if !e.IsValid() {
+		return fmt.Errorf("\"%s\" is not a valid StoryCategory", str)
+	}
 
 	return nil
 }