Add null checks in feedback processing pipeline (FRE-4514)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

services/spamshield/src/services/spamshield.service.ts

@@ -253,6 +253,18 @@ export class SpamShieldService {
       throw new Error('Feedback loop disabled via feature flag');
     }
 
+    if (!userId || typeof userId !== 'string' || userId.trim().length === 0) {
+      throw new Error('Feedback: userId is required');
+    }
+
+    if (!phoneNumber || typeof phoneNumber !== 'string') {
+      throw new Error('Feedback: phoneNumber must be a non-empty string');
+    }
+
+    if (typeof isSpam !== 'boolean') {
+      throw new Error('Feedback: isSpam must be a boolean');
+    }
+
     const validated = this.validatePhoneNumber(phoneNumber);
     const encrypted = FieldEncryptionService.encrypt(validated);
     const hash = FieldEncryptionService.hashPhoneNumber(validated);