fix(blacklist): handle invalid keywords gracefully (#1815)

* fix(blacklist): handle invalid keywords gracefully

* fix(blacklist): only remove keywords on 404 errors

* fix(blacklist): remove non-null assertion and add proper type annotation

* refactor(blacklist): return null instead of 404 for missing keywords

* fix(blacklist): add type annotation for validKeywords

* fix(selector): update type annotation for validKeywords

jellyseerr-api.yml

@@ -7324,11 +7324,22 @@ paths:
             example: 1
       responses:
         '200':
-          description: Keyword returned
+          description: Keyword returned (null if not found)
           content:
             application/json:
               schema:
+                nullable: true
                 $ref: '#/components/schemas/Keyword'
+        '500':
+          description: Internal server error
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  message:
+                    type: string
+                    example: 'Unable to retrieve keyword data.'
   /watchproviders/regions:
     get:
       summary: Get watch provider regions