fix #3505 daterange default DateTime should not serialize

src/Nest/CommonAbstractions/Infer/Field/Field.cs

@@ -18,7 +18,9 @@ public class Field : IEquatable<Field>, IUrlParameter
 		private readonly object _comparisonValue;
 		private readonly Type _type;
 
-		public Field(string name, double? boost = null, string format = null)
+		public Field(string name, double? boost = null) : this(name, boost, format: null) {}
+
+		public Field(string name, double? boost, string format = null)
 		{
 			name.ThrowIfNullOrEmpty(nameof(name));
 			Name = ParseFieldName(name, out var b);
@@ -27,7 +29,9 @@ public Field(string name, double? boost = null, string format = null)
 			_comparisonValue = Name;
 		}
 
-		public Field(Expression expression, double? boost = null, string format = null)
+		public Field(Expression expression, double? boost = null) : this(expression, boost, format: null) { }
+
+		public Field(Expression expression, double? boost, string format = null)
 		{
 			Expression = expression ?? throw new ArgumentNullException(nameof(expression));
 			Boost = boost;
@@ -37,7 +41,9 @@ public Field(Expression expression, double? boost = null, string format = null)
 			CachableExpression = !new HasVariableExpressionVisitor(expression).Found;
 		}
 
-		public Field(PropertyInfo property, double? boost = null, string format = null)
+		public Field(PropertyInfo property, double? boost = null) : this(property, boost, format: null) { }
+
+		public Field(PropertyInfo property, double? boost, string format = null)
 		{
 			Property = property ?? throw new ArgumentNullException(nameof(property));
 			Boost = boost;
@@ -98,13 +104,21 @@ string IUrlParameter.GetString(IConnectionConfigurationValues settings)
 
 		public Fields And(Field field) => new Fields(new[] { this, field });
 
-		public Fields And<T>(Expression<Func<T, object>> field, double? boost = null, string format = null) where T : class =>
+		public Fields And<T>(Expression<Func<T, object>> field, double? boost = null) where T : class =>
+			new Fields(new[] { this, new Field(field, boost, format: null) });
+
+		public Fields And<T>(Expression<Func<T, object>> field, double? boost, string format = null) where T : class =>
 			new Fields(new[] { this, new Field(field, boost, format) });
 
-		public Fields And(string field, double? boost = null, string format = null) =>
+		public Fields And(string field, double? boost = null) => new Fields(new[] { this, new Field(field, boost, format: null) });
+
+		public Fields And(string field, double? boost, string format = null) =>
 			new Fields(new[] { this, new Field(field, boost, format) });
 
-		public Fields And(PropertyInfo property, double? boost = null, string format = null) =>
+		public Fields And(PropertyInfo property, double? boost = null) =>
+			new Fields(new[] { this, new Field(property, boost, format: null) });
+
+		public Fields And(PropertyInfo property, double? boost, string format = null) =>
 			new Fields(new[] { this, new Field(property, boost, format) });
 
 		private static string ParseFieldName(string name, out double? boost)

src/Nest/CommonAbstractions/Static/Infer.cs

@@ -56,13 +56,17 @@ public static Fields Fields<T>(params Expression<Func<T, object>>[] fields) wher
 		/// Create a strongly typed string field name representation of the path to a property
 		/// <para>e.g. p => p.Array.First().SubProperty.Field will return 'array.subProperty.field'</para>
 		/// </summary>
-		public static Field Field<T>(Expression<Func<T, object>> path, double? boost = null, string format = null)
+		public static Field Field<T>(Expression<Func<T, object>> path, double? boost = null) where T : class => Field(path, boost, null);
+
+		public static Field Field<T>(Expression<Func<T, object>> path, double? boost, string format = null)
 			where T : class => new Field(path, boost, format);
 
-		public static Field Field(string field, double? boost = null, string format = null) =>
-			new Field(field, boost, format);
+		public static Field Field(string field, double? boost = null) => Field(field, boost, format: null);
+
+		public static Field Field(string field, double? boost, string format = null) => new Field(field, boost, format);
 
-		public static Field Field(PropertyInfo property, double? boost = null, string format = null) =>
+		public static Field Field(PropertyInfo property, double? boost = null) => Field(property, boost, format: null);
+		public static Field Field(PropertyInfo property, double? boost, string format = null) =>
 			new Field(property, boost, format);
 
 		public static PropertyName Property(string property) => property;

src/Nest/CommonOptions/DateMath/DateMath.cs

@@ -79,10 +79,11 @@ public static DateMath FromString(string dateMath)
 			return math;
 		}
 
+		internal bool IsValid => Self.Anchor.Match(d => d != default, s => !s.IsNullOrEmpty());
+
 		public override string ToString()
 		{
-			var isValid = Self.Anchor.Match(d => d != default(DateTime), s => !s.IsNullOrEmpty());
-			if (!isValid) return string.Empty;
+			if (!IsValid) return string.Empty;
 
 			var separator = Self.Round.HasValue || Self.Ranges.HasAny() ? "||" : string.Empty;
 

src/Nest/QueryDsl/TermLevel/Range/DateRangeQuery .cs

@@ -43,10 +43,10 @@ public class DateRangeQuery : FieldNameQueryBase, IDateRangeQuery
 		internal override void InternalWrapInContainer(IQueryContainer c) => c.Range = this;
 
 		internal static bool IsConditionless(IDateRangeQuery q) => q.Field.IsConditionless()
-			|| q.GreaterThanOrEqualTo == null
-			&& q.LessThanOrEqualTo == null
-			&& q.GreaterThan == null
-			&& q.LessThan == null;
+			|| ((q.GreaterThanOrEqualTo == null || !q.GreaterThanOrEqualTo.IsValid)
+			&& (q.LessThanOrEqualTo == null || !q.LessThanOrEqualTo.IsValid)
+			&& (q.GreaterThan == null || !q.GreaterThan.IsValid)
+			&& (q.LessThan == null || !q.LessThan.IsValid));
 	}
 
 	[JsonObject(MemberSerialization = MemberSerialization.OptIn)]

src/Tests/Tests.Reproduce/GithubIssue3538.cs

@@ -0,0 +1,95 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Elastic.Xunit.XunitPlumbing;
+using FluentAssertions;
+using Nest;
+using Nest.JsonNetSerializer;
+using Newtonsoft.Json;
+using Tests.Core.Client.Settings;
+
+namespace Tests.Reproduce
+{
+	public class GithubIssue3538
+	{
+		[U] public void EmptyPolicyCausesNullReferenceException()
+		{
+			var converter = new MyPocoJsonConverter();
+			var connectionSettings = new AlwaysInMemoryConnectionSettings(
+					sourceSerializerFactory: (builtin, settings) => new JsonNetSerializer(builtin, settings,
+						() =>
+						{
+							var jSettings = new JsonSerializerSettings();
+							jSettings.Converters.Add(converter);
+							return jSettings;
+						}))
+				.DefaultIndex("blah");
+
+			var client = new ElasticClient(connectionSettings);
+
+			var result = client.IndexDocument(new MyPoco() { Id = 1, Name = "x" });
+			converter.CanConvertCallCount.Should().Be(1);
+
+			client.Bulk(b => b.Index<MyPoco>(i=>i.Document(new MyPoco { Id = 2, Name = "y" })));
+			converter.CanConvertCallCount.Should().Be(2);
+
+			client.Bulk(b => b.Update<MyPoco>(i=>i.Doc(new MyPoco { Id = 3, Name = "z" })));
+			converter.CanConvertCallCount.Should().Be(3);
+
+			client.Bulk(b => b.Update<MyPoco>(i=>i.Upsert(new MyPoco { Id = 4, Name = "a" })));
+			converter.CanConvertCallCount.Should().Be(4);
+
+			converter.WriteCount.Should().Be(4);
+			converter.SeenIds.Should().BeEquivalentTo(1, 2, 3, 4);
+
+		}
+
+		public class MyPoco
+		{
+			public int Id { get; set; }
+			public string Name { get; set; }
+		}
+
+		public class MyPocoJsonConverter : JsonConverter
+		{
+			private int _canConvertCallCount;
+			public int CanConvertCallCount => _canConvertCallCount;
+
+			private int _writeCount;
+			public int WriteCount => _writeCount;
+
+			public List<int> SeenIds { get; } = new List<int>();
+
+
+			public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+			{
+				Interlocked.Increment(ref _writeCount);
+
+				if (!(value is MyPoco poco))
+				{
+					writer.WriteNull();
+					return;
+				}
+
+				writer.WriteStartObject();
+				writer.WritePropertyName("id");
+				writer.WriteValue(poco.Id);
+				SeenIds.Add(poco.Id);
+				writer.WritePropertyName("name");
+				writer.WriteValue(poco.Name);
+				writer.WriteEndObject();
+			}
+
+			public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) =>
+				new MyPoco { };
+
+			public override bool CanConvert(Type objectType)
+			{
+				Interlocked.Increment(ref _canConvertCallCount);
+
+				return objectType == typeof(MyPoco);
+			}
+		}
+	}
+}

src/Tests/Tests/ClientConcepts/HighLevel/Inference/FieldInference.doc.cs

@@ -500,7 +500,7 @@ public void PrecedenceIsAsExpected()
 			usingSettings.Expect("data").ForField(Field<Precedence>(p => p.DataMember));
 			usingSettings.Expect("DEFAULTFIELDNAMEINFERRER").ForField(Field<Precedence>(p => p.DefaultFieldNameInferrer));
 
-
+			var x = Field<Project>(p => p.Name, 1.0);
 			/** The same naming rules also apply when indexing a document */
 			usingSettings.Expect(new []
 			{

src/Tests/Tests/CommonOptions/DateMath/DateMathTests.cs

@@ -22,6 +22,17 @@ public void ImplicitConversionFromNullNullableDateTime()
 			dateMath.Should().BeNull();
 		}
 
+		[U] // F# backticks would be great in C# :)
+		public void ImplicitConversionFromDefaultDateTimeIsNotNullButEmptyString()
+		{
+			// in 6.x DateMath is backed by a DateTime instance
+			// for 7.x we will adress this
+			DateTime nullableDateTime = default;
+			Nest.DateMath dateMath = nullableDateTime;
+			dateMath.Should().NotBeNull();
+			dateMath.ToString().Should().BeEmpty();
+		}
+
 		[U]
 		public void ImplicitConversionFromDateMathString()
 		{
@@ -38,4 +49,5 @@ public void ImplicitConversionFromNullableDateTimeWithValue()
 			dateMath.Should().NotBeNull();
 		}
 	}
+
 }

src/Tests/Tests/QueryDsl/TermLevel/Range/DateRangeQueryUsageTests.cs

@@ -19,6 +19,13 @@ public DateRangeQueryUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) :
 				q.GreaterThanOrEqualTo = null;
 				q.LessThan = null;
 				q.LessThanOrEqualTo = null;
+			},
+			q =>
+			{
+				q.GreaterThan = default;
+				q.GreaterThanOrEqualTo = default;
+				q.LessThan = default;
+				q.LessThanOrEqualTo = default;
 			}
 		};
 
@@ -66,4 +73,5 @@ protected override QueryContainer QueryFluent(QueryContainerDescriptor<Project>
 				.TimeZone("+01:00")
 			);
 	}
+
 }

src/Tests/Tests/Search/Search/SearchApiTests.cs

@@ -272,8 +272,8 @@ public SearchApiDocValueFieldsTests(ReadOnlyCluster cluster, EndpointUsage usage
 				Field = "state",
 				Value = "Stable"
 			}),
-			DocValueFields = Infer.Field<Project>(p => p.Name, format: "use_field_mapping")
-				.And<Project>(p => p.LastActivity, format: "weekyear")
+			DocValueFields = Infer.Field<Project>(p => p.Name, boost: null, format: "use_field_mapping")
+				.And<Project>(p => p.LastActivity, boost: null, format: "weekyear")
 		};
 
 		protected override void ExpectResponse(ISearchResponse<Project> response)