[Backport master] Fix null-ref exception when track total hits is disabled (#5900)

* Fix null-ref exception when track total hits is disabled (#5898)

* Fixup

Co-authored-by: Steve Gordon <sgordon@hotmail.co.uk>

Author: github-actions[bot]

src/Nest/Search/Search/SearchResponse.cs

@@ -28,7 +28,8 @@ public interface ISearchResponse<out TDocument> : IResponse where TDocument : cl
 		ClusterStatistics Clusters { get; }
 
 		/// <summary>
-		/// Gets the documents inside the hits, by deserializing <see cref="IHitMetadata{T}.Source" /> into <typeparamref name="TDocument" />
+		/// Gets the documents inside the hits, by deserializing <see cref="IHitMetadata{T}.Source" /> into
+		/// <typeparamref name="TDocument" />
 		/// <para>
 		/// NOTE: if you use <see cref="ISearchRequest.StoredFields" /> on the search request,
 		/// <see cref="Documents" /> will be empty and you should use <see cref="Fields" />
@@ -68,6 +69,11 @@ public interface ISearchResponse<out TDocument> : IResponse where TDocument : cl
 		/// </summary>
 		long NumberOfReducePhases { get; }
 
+		/// <summary>
+		/// When a search is made over a point in time, this will be the ID of the point in time.
+		/// </summary>
+		string PointInTimeId { get; }
+
 		/// <summary>
 		/// Gets the results of profiling the search query. Has a value only when
 		/// <see cref="ISearchRequest.Profile" /> is set to <c>true</c> on the search request.
@@ -110,11 +116,6 @@ public interface ISearchResponse<out TDocument> : IResponse where TDocument : cl
 		/// Gets the total number of documents matching the search query criteria
 		/// </summary>
 		long Total { get; }
-
-		/// <summary>
-		/// When a search is made over a point in time, this will be the ID of the point in time.
-		/// </summary>
-		string PointInTimeId { get; }
 	}
 
 	public class SearchResponse<TDocument> : ResponseBase, ISearchResponse<TDocument> where TDocument : class
@@ -126,7 +127,7 @@ public class SearchResponse<TDocument> : ResponseBase, ISearchResponse<TDocument
 		private IReadOnlyCollection<IHit<TDocument>> _hits;
 
 		/// <inheritdoc />
-		[DataMember(Name ="aggregations")]
+		[DataMember(Name = "aggregations")]
 		public AggregateDictionary Aggregations { get; internal set; } = AggregateDictionary.Default;
 
 		/// <inheritdoc />
@@ -153,51 +154,51 @@ public class SearchResponse<TDocument> : ResponseBase, ISearchResponse<TDocument
 			_hits ?? (_hits = HitsMetadata?.Hits ?? EmptyReadOnly<IHit<TDocument>>.Collection);
 
 		/// <inheritdoc />
-		[DataMember(Name ="hits")]
+		[DataMember(Name = "hits")]
 		public IHitsMetadata<TDocument> HitsMetadata { get; internal set; }
 
 		/// <inheritdoc />
 		[IgnoreDataMember]
 		public double MaxScore => HitsMetadata?.MaxScore ?? 0;
 
 		/// <inheritdoc />
-		[DataMember(Name ="num_reduce_phases")]
+		[DataMember(Name = "num_reduce_phases")]
 		public long NumberOfReducePhases { get; internal set; }
 
 		/// <inheritdoc />
-		[DataMember(Name ="profile")]
+		[DataMember(Name = "pit_id")]
+		public string PointInTimeId { get; internal set; }
+
+		/// <inheritdoc />
+		[DataMember(Name = "profile")]
 		public Profile Profile { get; internal set; }
 
 		/// <inheritdoc />
 		[DataMember(Name = "_scroll_id")]
 		public string ScrollId { get; internal set; }
 
 		/// <inheritdoc />
-		[DataMember(Name ="_shards")]
+		[DataMember(Name = "_shards")]
 		public ShardStatistics Shards { get; internal set; }
 
 		/// <inheritdoc />
-		[DataMember(Name ="suggest")]
+		[DataMember(Name = "suggest")]
 		public ISuggestDictionary<TDocument> Suggest { get; internal set; } = SuggestDictionary<TDocument>.Default;
 
 		/// <inheritdoc />
-		[DataMember(Name ="terminated_early")]
+		[DataMember(Name = "terminated_early")]
 		public bool TerminatedEarly { get; internal set; }
 
 		/// <inheritdoc />
-		[DataMember(Name ="timed_out")]
+		[DataMember(Name = "timed_out")]
 		public bool TimedOut { get; internal set; }
 
 		/// <inheritdoc />
-		[DataMember(Name ="took")]
+		[DataMember(Name = "took")]
 		public long Took { get; internal set; }
 
 		/// <inheritdoc />
 		[IgnoreDataMember]
-		public long Total => HitsMetadata?.Total.Value ?? -1;
-
-		/// <inheritdoc />
-		[DataMember(Name = "pit_id")]
-		public string PointInTimeId { get; internal set; }
+		public long Total => HitsMetadata?.Total?.Value ?? -1;
 	}
 }

tests/Tests.Reproduce/GitHubIssue5892.cs

@@ -0,0 +1,40 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System.Text;
+using Elastic.Elasticsearch.Xunit.XunitPlumbing;
+using FluentAssertions;
+using Nest;
+using Tests.Core.Client;
+using Tests.Domain;
+
+namespace Tests.Reproduce
+{
+	public class GitHubIssue5892
+	{
+		private static readonly byte[] ResponseBytes = Encoding.UTF8.GetBytes(@"{
+    ""took"": 2,
+    ""timed_out"": false,
+    ""_shards"": {
+        ""total"": 1,
+        ""successful"": 1,
+        ""skipped"": 0,
+        ""failed"": 0
+    },
+    ""hits"": {
+        ""max_score"": null,
+        ""hits"": []
+    }
+}");
+
+		[U] public void SearchResponseTotalShouldNotThrowWhenTrackTotalHitsIsFalse()
+		{
+			var client = TestClient.FixedInMemoryClient(ResponseBytes);
+			
+			var response = client.Search<Project>(s => s.Index("test").MatchAll());
+
+			response.Total.Should().Be(-1);
+		}
+	}
+}