fix #2812 make sure verbatim sends an empty array (#2941)

Conflicts:
	src/Nest/QueryDsl/TermLevel/Terms/TermsQueryJsonConverter.cs
	src/Tests/QueryDsl/TermLevel/Terms/TermsQueryUsageTests.cs

Author: Mpdreamz

src/Nest/QueryDsl/TermLevel/Terms/TermsQueryJsonConverter.cs

@@ -14,23 +14,38 @@ internal class TermsQueryJsonConverter : JsonConverter
 
 		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
 		{
-			var t = value as ITermsQuery;
-			if (t == null) return;
+			if (!(value is ITermsQuery t)) return;
 
 			var settings = serializer.GetConnectionSettings();
 			var field = settings.Inferrer.Field(t.Field);
 
 			writer.WriteStartObject();
 			{
-				if (t.Terms.HasAny())
+				if (t.IsVerbatim)
 				{
-					writer.WritePropertyName(field);
-					serializer.Serialize(writer, t.Terms);
+                    if (t.TermsLookup != null)
+                    {
+                        writer.WritePropertyName(field);
+                        serializer.Serialize(writer, t.TermsLookup);
+                    }
+                    else if (t.Terms != null)
+                    {
+                        writer.WritePropertyName(field);
+                        serializer.Serialize(writer, t.Terms);
+                    }
 				}
-				else if (t.TermsLookup != null)
+				else
 				{
-					writer.WritePropertyName(field);
-					serializer.Serialize(writer, t.TermsLookup);
+                    if (t.Terms.HasAny())
+                    {
+                        writer.WritePropertyName(field);
+                        serializer.Serialize(writer, t.Terms);
+                    }
+                    else if (t.TermsLookup != null)
+                    {
+                        writer.WritePropertyName(field);
+                        serializer.Serialize(writer, t.TermsLookup);
+                    }
 				}
 #pragma warning disable 618
 				if (t.DisableCoord.HasValue)

src/Tests/QueryDsl/QueryDslUsageTestsBase.cs

@@ -57,7 +57,7 @@ private void AssertIsNotConditionless(IQueryContainer c)
 
 		protected QueryContainer ConditionlessQuery = new QueryContainer(new TermQuery { });
 
-		protected QueryContainer VerbatimQuery = new QueryContainer(new TermQuery { IsVerbatim = true });
+		protected readonly QueryContainer VerbatimQuery = new QueryContainer(new TermQuery { IsVerbatim = true });
 
 		[U] public void SeenByVisitor()
 		{

src/Tests/QueryDsl/TermLevel/Term/TermQueryUsageTests.cs

@@ -45,4 +45,45 @@ protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project>
 			q=> q.Value = null
 		};
 	}
+
+	/**[float]
+	*== Verbatim term query
+	 *
+	 * By default an empty term is conditionless so will be rewritten. Sometimes sending an empty term to
+	 * match nothing makes sense. You can either use the `ConditionlessQuery` construct from NEST to provide a fallback or make the
+	 * query verbatim as followed:
+	*/
+	public class VerbatimTermQueryUsageTests : TermQueryUsageTests
+	{
+		public VerbatimTermQueryUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cluster, usage) { }
+
+		protected override ConditionlessWhen ConditionlessWhen => null;
+		//when reading back the json the notion of is conditionless is lost
+		protected override bool SupportsDeserialization => false;
+
+		protected override object QueryJson => new
+		{
+			term = new
+			{
+				description = new
+				{
+					value = ""
+				}
+			}
+		};
+
+		protected override QueryContainer QueryInitializer => new TermQuery
+		{
+			IsVerbatim = true,
+			Field = "description",
+			Value = "",
+		};
+
+		protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project> q) => q
+			.Term(c => c
+				.Verbatim()
+				.Field(p => p.Description)
+				.Value(string.Empty)
+			);
+	}
 }

src/Tests/QueryDsl/TermLevel/Terms/TermsQueryUsageTests.cs

@@ -80,4 +80,44 @@ protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project>
 				.Terms("term1")
 			);
 	}
+
+	/**[float]
+	*== Verbatim terms query
+	 *
+	 * By default an empty terms array is conditionless so will be rewritten. Sometimes sending an empty an empty array to mean
+	 * match nothing makes sense. You can either use the `ConditionlessQuery` construct from NEST to provide a fallback or make the
+	 * query verbatim as followed:
+	*/
+	public class VerbatimTermsQueryUsageTests : TermsQueryUsageTests
+	{
+		public VerbatimTermsQueryUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cluster, usage) { }
+
+		protected override ConditionlessWhen ConditionlessWhen => null;
+		//when reading back the json the notion of is conditionless is lost
+		protected override bool SupportsDeserialization => false;
+
+		protected override object QueryJson => new
+		{
+			terms = new
+			{
+				description = new string[] {}
+			}
+		};
+
+		protected override QueryContainer QueryInitializer => new TermsQuery
+		{
+			IsVerbatim = true,
+			Field = "description",
+			Terms = new string[] {},
+		};
+
+		protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project> q) => q
+			.Terms(c => c
+				.Verbatim()
+				.Field(p => p.Description)
+				.Terms(new string[] {})
+			);
+	}
+
+
 }