Optimize empty arrays usages

src/NHibernate.DomainModel/Async/CustomPersister.cs

@@ -21,6 +21,7 @@
 using NHibernate.Tuple.Entity;
 using NHibernate.Type;
 using NHibernate.Util;
+using Array = System.Array;
 
 namespace NHibernate.DomainModel
 {

src/NHibernate.DomainModel/Baz.cs

@@ -396,7 +396,7 @@ public void SetDefaults()
 			StringArray = StringSet.ToArray();
 			StringList = new List<string>(StringArray);
 			IntArray = new int[] {1, 3, 3, 7};
-			FooArray = new Foo[0];
+			FooArray = Array.Empty<Foo>();
 
 			Customs = new List<string[]>();
 			Customs.Add(new String[] {"foo", "bar"});

src/NHibernate.DomainModel/CustomPersister.cs

@@ -11,6 +11,7 @@
 using NHibernate.Tuple.Entity;
 using NHibernate.Type;
 using NHibernate.Util;
+using Array = System.Array;
 
 namespace NHibernate.DomainModel
 {
@@ -130,12 +131,12 @@ public bool[] PropertyInsertability
 
 		public ValueInclusion[] PropertyInsertGenerationInclusions
 		{
-			get { return new ValueInclusion[0]; }
+			get { return Array.Empty<ValueInclusion>(); }
 		}
 
 		public ValueInclusion[] PropertyUpdateGenerationInclusions
 		{
-			get { return new ValueInclusion[0]; }
+			get { return Array.Empty<ValueInclusion>(); }
 		}
 
 		public bool[] PropertyCheckability

src/NHibernate.Test/Async/Component/Basic/ComponentTest.cs

@@ -32,7 +32,7 @@ protected override string MappingsAssembly
 
 		protected override System.Collections.IList Mappings
 		{
-			get { return new string[] { }; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override void Configure(Configuration configuration)

src/NHibernate.Test/Async/DialectTest/DialectFixture.cs

@@ -68,7 +68,7 @@ public async Task CurrentTimestampSelectionAsync()
 
 			using (var connection = await (sessions.ConnectionProvider.GetConnectionAsync(CancellationToken.None)))
 			{
-				var statement = driver.GenerateCommand(CommandType.Text, new SqlString(dialect.CurrentTimestampSelectString), new SqlType[0]);
+				var statement = driver.GenerateCommand(CommandType.Text, new SqlString(dialect.CurrentTimestampSelectString), Array.Empty<SqlType>());
 				statement.Connection = connection;
 				using (var reader = await (statement.ExecuteReaderAsync()))
 				{

src/NHibernate.Test/Async/Events/PostEvents/PostUpdateFixture.cs

@@ -8,6 +8,7 @@
 //------------------------------------------------------------------------------
 
 
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using NHibernate.Event;
@@ -56,7 +57,7 @@ public async Task ImplicitFlushAsync()
 			}
 
 			await (DbCleanupAsync());
-			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = new IPostUpdateEventListener[0];
+			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = Array.Empty<IPostUpdateEventListener>();
 		}
 
 		[Test]
@@ -85,7 +86,7 @@ public async Task ExplicitUpdateAsync()
 			}
 
 			await (DbCleanupAsync());
-			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = new IPostUpdateEventListener[0];
+			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = Array.Empty<IPostUpdateEventListener>();
 		}
 
 		[Test]
@@ -123,7 +124,7 @@ public async Task WithDetachedObjectAsync()
 			}
 
 			await (DbCleanupAsync());
-			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = new IPostUpdateEventListener[0];
+			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = Array.Empty<IPostUpdateEventListener>();
 		}
 
 		[Test]
@@ -163,7 +164,7 @@ public async Task UpdateDetachedObjectAsync()
 			}
 
 			await (DbCleanupAsync());
-			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = new IPostUpdateEventListener[0];
+			((DebugSessionFactory) Sfi).EventListeners.PostUpdateEventListeners = Array.Empty<IPostUpdateEventListener>();
 		}
 
 		[Test]
@@ -202,7 +203,7 @@ public async Task UpdateDetachedObjectWithLockAsync()
 			}
 
 			await (DbCleanupAsync());
-			((DebugSessionFactory)Sfi).EventListeners.PostUpdateEventListeners = new IPostUpdateEventListener[0];
+			((DebugSessionFactory)Sfi).EventListeners.PostUpdateEventListeners = Array.Empty<IPostUpdateEventListener>();
 		}
 		private async Task DbCleanupAsync(CancellationToken cancellationToken = default(CancellationToken))
 		{

src/NHibernate.Test/Async/ExceptionsTest/NullQueryTest.cs

@@ -28,7 +28,7 @@ public class NullQueryTestAsync : TestCase
 
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		#endregion

src/NHibernate.Test/Async/Legacy/FumTest.cs

@@ -86,7 +86,7 @@ public async Task CriteriaCollectionAsync()
 				Assert.IsTrue(b.MapComponent.Stringmap.Count == 2);
 
 				int none = (await (s.CreateCriteria(typeof(Fum))
-					.Add(Expression.In("FumString", new string[0]))
+					.Add(Expression.In("FumString", Array.Empty<string>()))
 					.ListAsync())).Count;
 				Assert.AreEqual(0, none);
 

src/NHibernate.Test/Async/LinqBulkManipulation/Fixture.cs

@@ -25,7 +25,7 @@ namespace NHibernate.Test.LinqBulkManipulation
 	[TestFixture]
 	public class FixtureAsync : TestCase
 	{
-		protected override IList Mappings => new string[0];
+		protected override IList Mappings => Array.Empty<string>();
 
 		protected override void Configure(Cfg.Configuration configuration)
 		{
@@ -970,7 +970,7 @@ public async Task SimpleDeleteOnAnimalAsync()
 			using (var t = s.BeginTransaction())
 			{
 				// Get rid of FK which may fail the test
-				_doll.Friends = new Human[0];
+				_doll.Friends = Array.Empty<Human>();
 				await (s.UpdateAsync(_doll));
 				await (t.CommitAsync());
 			}
@@ -1029,7 +1029,7 @@ public async Task DeleteOnJoinedSubclassAsync()
 			using (var t = s.BeginTransaction())
 			{
 				// Get rid of FK which may fail the test
-				_doll.Friends = new Human[0];
+				_doll.Friends = Array.Empty<Human>();
 				await (s.UpdateAsync(_doll));
 				await (t.CommitAsync());
 			}

src/NHibernate.Test/Async/MappingByCode/IntegrationTests/NH2825/FixtureByCode.cs

@@ -8,6 +8,7 @@
 //------------------------------------------------------------------------------
 
 
+using System;
 using System.Collections;
 using NHibernate.Cfg.MappingSchema;
 using NHibernate.Mapping.ByCode;
@@ -21,7 +22,7 @@ public class FixtureByCodeAsync : FixtureAsync
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override string MappingsAssembly
@@ -63,4 +64,4 @@ private HbmMapping GetMappings()
 			return mapper.CompileMappingForAllExplicitlyAddedEntities();
 		}
 	}
-}
+}

src/NHibernate.Test/Async/NHSpecificTest/EmptyMappingsFixture.cs

@@ -29,7 +29,7 @@ public class EmptyMappingsFixtureAsync : TestCase
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		[Test]

src/NHibernate.Test/Async/NHSpecificTest/NH1421/Fixture.cs

@@ -27,7 +27,7 @@ public void WhenParameterListIsEmptyUsingQueryThenDoesNotTrowsNullReferenceExcep
 			using (var s = OpenSession())
 			{
 				var query = s.CreateQuery("from AnEntity a where a.id in (:myList)");
-				Assert.That(() => query.SetParameterList("myList", new long[0]).ListAsync(), Throws.Exception.Not.InstanceOf<NullReferenceException>());
+				Assert.That(() => query.SetParameterList("myList", Array.Empty<long>()).ListAsync(), Throws.Exception.Not.InstanceOf<NullReferenceException>());
 			}
 		}
 	}

src/NHibernate.Test/Async/NHSpecificTest/NH2166/Fixture.cs

@@ -21,7 +21,7 @@ public class FixtureAsync: TestCase
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		[Test]

src/NHibernate.Test/Async/NHSpecificTest/NH4077/PostInsertFixture.cs

@@ -74,7 +74,7 @@ protected override HbmMapping GetMappings()
 		protected override void Configure(Configuration configuration)
 		{
 			base.Configure(configuration);
-			var existingListeners = (configuration.EventListeners.PostInsertEventListeners ?? new IPostInsertEventListener[0]).ToList();
+			var existingListeners = (configuration.EventListeners.PostInsertEventListeners ?? Array.Empty<IPostInsertEventListener>()).ToList();
 			// this evil listener uses the session to perform a few queries and causes an auto-flush to happen
 			existingListeners.Add(new CausesAutoflushListener());
 			configuration.EventListeners.PostInsertEventListeners = existingListeners.ToArray();

src/NHibernate.Test/Async/NHSpecificTest/NH4077/PostUpdateFixture.cs

@@ -68,7 +68,7 @@ protected override HbmMapping GetMappings()
 		protected override void Configure(Configuration configuration)
 		{
 			base.Configure(configuration);
-			var existingListeners = (configuration.EventListeners.PostUpdateEventListeners ?? new IPostUpdateEventListener[0]).ToList();
+			var existingListeners = (configuration.EventListeners.PostUpdateEventListeners ?? Array.Empty<IPostUpdateEventListener>()).ToList();
 			// this evil listener uses the session to perform a few queries and causes an auto-flush to happen
 			existingListeners.Add(new CausesAutoflushListener());
 			configuration.EventListeners.PostUpdateEventListeners = existingListeners.ToArray();

src/NHibernate.Test/Async/NHSpecificTest/NH901/Fixture.cs

@@ -8,6 +8,7 @@
 //------------------------------------------------------------------------------
 
 
+using System;
 using System.Collections;
 using NHibernate.Cfg;
 using NHibernate.Mapping.ByCode;
@@ -118,7 +119,7 @@ public class FixtureByCodeAsync : FixtureBaseAsync
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override string MappingsAssembly

src/NHibernate.Test/Async/SecondLevelCacheTest/InvalidationTests.cs

@@ -14,7 +14,6 @@
 using System.Reflection;
 using NHibernate.Cache;
 using NHibernate.Cfg;
-using NHibernate.Engine;
 using NHibernate.Impl;
 using NHibernate.Test.SecondLevelCacheTests;
 using NSubstitute;

src/NHibernate.Test/Async/TestTestCase.cs

@@ -23,7 +23,7 @@ public class TestTestCaseAsync : TestCase
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		private bool _failOnTearDown;

src/NHibernate.Test/Async/TransactionTest/TransactionNotificationFixture.cs

@@ -8,6 +8,7 @@
 //------------------------------------------------------------------------------
 
 
+using System;
 using System.Collections;
 using System.Data.Common;
 using NUnit.Framework;
@@ -21,7 +22,7 @@ public class TransactionNotificationFixtureAsync : TestCase
 	{
 		protected override IList Mappings
 		{
-			get { return new string[] {}; }
+			get { return Array.Empty<string>(); }
 		}
 
 		[Test]
@@ -99,4 +100,4 @@ public async Task ShouldNotifyAfterTransactionWithOwnConnectionAsync(bool usePre
 			Assert.That(interceptor.afterTransactionCompletionCalled, Is.EqualTo(1));
 		}
 	}
-}
+}

src/NHibernate.Test/Async/TypesTest/BinaryBlobTypeFixture.cs

@@ -69,7 +69,7 @@ public async Task ReadWriteZeroLenAsync()
 			using (ISession s = OpenSession())
 			{
 				BinaryBlobClass b = new BinaryBlobClass();
-				b.BinaryBlob = new byte[0];
+				b.BinaryBlob = Array.Empty<byte>();
 				savedId = await (s.SaveAsync(b));
 				await (s.FlushAsync());
 			}

src/NHibernate.Test/Async/TypesTest/BinaryTypeFixture.cs

@@ -78,8 +78,8 @@ public async Task InsertZeroLengthAsync()
 			BinaryClass bcBinary = new BinaryClass();
 			bcBinary.Id = 1;
 
-			bcBinary.DefaultSize = new byte[0];
-			bcBinary.WithSize = new byte[0];
+			bcBinary.DefaultSize = Array.Empty<byte>();
+			bcBinary.WithSize = Array.Empty<byte>();
 
 			ISession s = OpenSession();
 			ITransaction t = s.BeginTransaction();

src/NHibernate.Test/BulkManipulation/BaseFixture.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections;
 using NHibernate.Hql.Ast.ANTLR;
 using System.Collections.Generic;
@@ -13,7 +14,7 @@ public class BaseFixture: TestCase
 
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		#endregion
@@ -38,4 +39,4 @@ public string GetSql(string query)
 			return qt.SQLString;
 		}
 	}
-}
+}

src/NHibernate.Test/Cascade/OneToOneCascadeDelete/Fk/Bidirectional/DeleteOneToOneOrphansTest.cs

@@ -1,4 +1,5 @@
-using System.Collections;
+using System;
+using System.Collections;
 using NHibernate.Cfg;
 using NHibernate.Mapping.ByCode;
 using NUnit.Framework;
@@ -92,7 +93,7 @@ public class DeleteOneToOneOrphansTestByCode : DeleteOneToOneOrphansTest
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override void AddMappings(Configuration configuration)

src/NHibernate.Test/Cascade/OneToOneCascadeDelete/Fk/Composite/DeleteOneToOneOrphansTest.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections;
 using NHibernate.Cfg.MappingSchema;
 using NHibernate.Mapping.ByCode;
@@ -93,7 +94,7 @@ public class DeleteOneToOneOrphansTestByCode : DeleteOneToOneOrphansTest
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 

src/NHibernate.Test/Cascade/OneToOneCascadeDelete/Fk/Reversed/Bidirectional/DeleteOneToOneOrphansTest.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections;
 using NHibernate.Cfg;
 using NHibernate.Mapping.ByCode;
@@ -92,7 +93,7 @@ public class DeleteOneToOneOrphansTestByCode : DeleteOneToOneOrphansTest
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override void AddMappings(Configuration configuration)

src/NHibernate.Test/Cascade/OneToOneCascadeDelete/Fk/Reversed/Unidirectional/DeleteOneToOneOrphansTest.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections;
 using NHibernate.Cfg;
 using NHibernate.Mapping.ByCode;
@@ -142,7 +143,7 @@ public class DeleteOneToOneOrphansTestByCode : DeleteOneToOneOrphansTest
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override void AddMappings(Configuration configuration)

src/NHibernate.Test/Cascade/OneToOneCascadeDelete/Pk/Bidirectional/DeleteOneToOneOrphansTest.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections;
 using NHibernate.Cfg;
 using NHibernate.Mapping.ByCode;
@@ -95,7 +96,7 @@ public class DeleteOneToOneOrphansTestByCode : DeleteOneToOneOrphansTest
 	{
 		protected override IList Mappings
 		{
-			get { return new string[0]; }
+			get { return Array.Empty<string>(); }
 		}
 
 		protected override void AddMappings(Configuration configuration)