Improved nullability.

Author: Oren (electricessence)

IElement.cs

@@ -1,7 +1,12 @@
-namespace Open.Hierarchy
+using System.Diagnostics.CodeAnalysis;
+
+namespace Open.Hierarchy
 {
 	public interface IElement<T>
 	{
+#if NETSTANDARD2_1
+		[AllowNull]
+#endif
 		T Value { get; set; }
 	}
 }

Node.Factory.cs

@@ -1,5 +1,6 @@
 using Open.Disposable;
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
 
 namespace Open.Hierarchy
@@ -56,6 +57,9 @@ public Node<T> GetNodeWithValue(T value, bool asUnmapped = false)
 			/// </summary>
 			/// <param name="node">The node to be recycled.</param>
 			/// <returns>The value contained in the node.</returns>
+#if NETSTANDARD2_1
+			[return: MaybeNull]
+#endif
 			public T Recycle(Node<T> node)
 			{
 				if (node == null) throw new ArgumentNullException(nameof(node));
@@ -66,6 +70,9 @@ public T Recycle(Node<T> node)
 				return RecycleInternal(node);
 			}
 
+#if NETSTANDARD2_1
+			[return: MaybeNull]
+#endif
 			internal T RecycleInternal(Node<T> n)
 			{
 				var value = n.Value;

Node.cs

@@ -30,13 +30,16 @@ void AssertNotRecycled()
 				throw new InvalidOperationException("Attempting to modify a node that has been recyled.");
 		}
 
-		// ReSharper disable once UnusedAutoPropertyAccessor.Global
+#if NETSTANDARD2_1
+		[AllowNull]
+#endif
+		private T _value;
+
 		/// <summary>
 		/// The value for the node to hold on to.
 		/// </summary>
-		private T _value;
 #if NETSTANDARD2_1
-		[MaybeNull]
+		[AllowNull]
 #endif
 		public T Value
 		{
@@ -312,6 +315,9 @@ public void TeardownChildren()
 		/// <summary>
 		/// Recycles this node.
 		/// </summary>
+#if NETSTANDARD2_1
+		[return: MaybeNull]
+#endif
 		// ReSharper disable once UnusedMethodReturnValue.Global
 		public T Recycle()
 		{

Open.Hierarchy.csproj

@@ -16,7 +16,7 @@
 		<RepositoryUrl>https://github.com/electricessence/Open.Hierarchy/</RepositoryUrl>
 		<RepositoryType>git</RepositoryType>
 		<PackageTags>dotnet, dotnetcore, cs, tree, node, hierarchy, parent, child, root</PackageTags>
-		<Version>1.7.1</Version>
+		<Version>1.7.2</Version>
 		<PackageReleaseNotes></PackageReleaseNotes>
 		<PackageLicenseExpression>MIT</PackageLicenseExpression>
 		<Nullable>enable</Nullable>