MutateIn.ArrayInsert throws PathInvalidException

 public async Task Test_MutateInAsync_ArrayInsert()

        {

            var col = await GetDefaultCollection();

            var doc1 = Guid.NewGuid().ToString();            await col.UpsertAsync(doc1, new { Name = doc1, Id = 1, Items = new[] { 1, 2, 3 } },

                options => options.Expiry(TimeSpan.FromSeconds(2)));            var result = await col.MutateInAsync(doc1, specs => specs.ArrayInsert("items", new[] {8, 9}));

            Assert.True(result.Cas > 0);            var result1 = await col.GetAsync(doc1);

            var content = result1.ContentAs<JObject>();

            Assert.Contains(8, content?.SelectToken("items").ToObject<List<int>>());

            Assert.Contains(9, content?.SelectToken("items").ToObject<List<int>>());

        } 

Couchbase.Core.Exceptions.KeyValue.PathInvalidException
Exception of type 'Couchbase.Core.Exceptions.KeyValue.PathInvalidException' was thrown.
   at Couchbase.Core.ClusterNode.ExecuteOp(Func`4 sender, IOperation op, Object state, CancellationTokenPair tokenPair) in C:\Users\Jeff Morris\source\couchbase-net-client\src\Couchbase\Core\ClusterNode.cs:line 585
   at Couchbase.CouchbaseBucket.SendAsync(IOperation op, CancellationTokenPair tokenPair) in C:\Users\Jeff Morris\source\couchbase-net-client\src\Couchbase\CouchbaseBucket.cs:line 212
   at Couchbase.Core.Retry.RetryOrchestrator.RetryAsync(BucketBase bucket, IOperation operation, CancellationTokenPair tokenPair) in C:\Users\Jeff Morris\source\couchbase-net-client\src\Couchbase\Core\Retry\RetryOrchestrator.cs:line 181
   at Couchbase.KeyValue.CouchbaseCollection.MutateInAsync(String id, IEnumerable`1 specs, MutateInOptions options) in C:\Users\Jeff Morris\source\couchbase-net-client\src\Couchbase\KeyValue\CouchbaseCollection.cs:line 708
   at Couchbase.CombinationTests.Tests.KeyValue.KeyValueTests.Test_MutateInAsync_ArrayInsert() in C:\Users\Jeff Morris\source\couchbase-net-client\tests\Couchbase.CombinationTests\Tests\KeyValue\KeyValueTests.cs:line 365