Do a null check before returning the primary providers

Test: local build
Bug: 280492574

Change-Id: I0182c2060fbe5c74027785d539671f9eaaaf2a25

services/credentials/java/com/android/server/credentials/CredentialManagerService.java

@@ -290,6 +290,9 @@ public final class CredentialManagerService
                 mContext, Settings.Secure.CREDENTIAL_SERVICE_PRIMARY,
                 /* isMultipleMode= */ true);
         String[] serviceNames = resolver.readServiceNameList(resolvedUserId);
+        if (serviceNames == null) {
+            return new HashSet<String>();
+        }
         return new HashSet<String>(Arrays.asList(serviceNames));
     }