fix bug in settings resolver

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 ### Changed
 ### Fixed
+
+- bug in settings resolver with nullable fields
+
 ### Security
 
 - container now runs as non root user

src/dto/setting/setting.model.ts

@@ -5,8 +5,8 @@ export class SettingModel {
   @Field(() => ID)
   readonly key: string
 
-  @Field()
-  readonly value: string
+  @Field({ nullable: true })
+  readonly value?: string
 
   @Field()
   readonly isTrue: boolean