Adding null check for implicit cast from array to Span. (#25257)

* Adding null check for implicit cast from array to Span.

* Addressing PR feedback - adding check for ArraySegment

src/System.Memory/src/System/ReadOnlySpan.cs

@@ -242,12 +242,13 @@ public override int GetHashCode()
         /// <summary>
         /// Defines an implicit conversion of an array to a <see cref="ReadOnlySpan{T}"/>
         /// </summary>
-        public static implicit operator ReadOnlySpan<T>(T[] array) => new ReadOnlySpan<T>(array);
+        public static implicit operator ReadOnlySpan<T>(T[] array) => array != null ? new ReadOnlySpan<T>(array) : default;
 
         /// <summary>
         /// Defines an implicit conversion of a <see cref="ArraySegment{T}"/> to a <see cref="ReadOnlySpan{T}"/>
         /// </summary>
-        public static implicit operator ReadOnlySpan<T>(ArraySegment<T> arraySegment) => new ReadOnlySpan<T>(arraySegment.Array, arraySegment.Offset, arraySegment.Count);
+        public static implicit operator ReadOnlySpan<T>(ArraySegment<T> arraySegment)
+            => arraySegment.Array != null ? new ReadOnlySpan<T>(arraySegment.Array, arraySegment.Offset, arraySegment.Count) : default;
 
         /// <summary>
         /// Forms a slice out of the given read-only span, beginning at 'start'.

src/System.Memory/src/System/Span.cs

@@ -348,12 +348,13 @@ public override int GetHashCode()
         /// <summary>
         /// Defines an implicit conversion of an array to a <see cref="Span{T}"/>
         /// </summary>
-        public static implicit operator Span<T>(T[] array) => new Span<T>(array);
+        public static implicit operator Span<T>(T[] array) => array != null ? new Span<T>(array) : default;
 
         /// <summary>
         /// Defines an implicit conversion of a <see cref="ArraySegment{T}"/> to a <see cref="Span{T}"/>
         /// </summary>
-        public static implicit operator Span<T>(ArraySegment<T> arraySegment) => new Span<T>(arraySegment.Array, arraySegment.Offset, arraySegment.Count);
+        public static implicit operator Span<T>(ArraySegment<T> arraySegment)
+            => arraySegment.Array != null ? new Span<T>(arraySegment.Array, arraySegment.Offset, arraySegment.Count) : default;
 
         /// <summary>
         /// Defines an implicit conversion of a <see cref="Span{T}"/> to a <see cref="ReadOnlySpan{T}"/>

src/System.Memory/tests/ReadOnlySpan/ImplicitConversion.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Xunit;
+
+namespace System.SpanTests
+{
+    public static partial class ReadOnlySpanTests
+    {
+        [Fact]
+        public static void NullImplicitCast()
+        {
+            int[] dst = null;
+            ReadOnlySpan<int> srcSpan = dst;
+            Assert.True(ReadOnlySpan<int>.Empty == srcSpan);
+        }
+
+        [Fact]
+        public static void ArraySegmentDefaultImplicitCast()
+        {
+            ArraySegment<int> dst = default;
+            ReadOnlySpan<int> srcSpan = dst;
+            Assert.True(ReadOnlySpan<int>.Empty == srcSpan);
+        }
+    }
+}

src/System.Memory/tests/Span/ImplicitConversion.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Xunit;
+
+namespace System.SpanTests
+{
+    public static partial class SpanTests
+    {
+        [Fact]
+        public static void NullImplicitCast()
+        {
+            int[] dst = null;
+            Span<int> srcSpan = dst;
+            Assert.True(Span<int>.Empty == srcSpan);
+        }
+
+        [Fact]
+        public static void ArraySegmentDefaultImplicitCast()
+        {
+            ArraySegment<int> dst = default;
+            Span<int> srcSpan = dst;
+            Assert.True(Span<int>.Empty == srcSpan);
+        }
+    }
+}

src/System.Memory/tests/System.Memory.Tests.csproj

@@ -29,6 +29,7 @@
     <Compile Include="Span\GcReporting.cs" />
     <Compile Include="Span\GetEnumerator.cs" />
     <Compile Include="Span\GetHashCode.cs" />
+    <Compile Include="Span\ImplicitConversion.cs" />
     <Compile Include="Span\IndexOf.T.cs" />
     <Compile Include="Span\IndexOf.byte.cs" />
     <Compile Include="Span\IndexOf.char.cs" />
@@ -58,6 +59,7 @@
     <Compile Include="ReadOnlySpan\Equality.cs" />
     <Compile Include="ReadOnlySpan\GetEnumerator.cs" />
     <Compile Include="ReadOnlySpan\GetHashCode.cs" />
+    <Compile Include="ReadOnlySpan\ImplicitConversion.cs" />
     <Compile Include="ReadOnlySpan\IndexOf.T.cs" />
     <Compile Include="ReadOnlySpan\IndexOf.byte.cs" />
     <Compile Include="ReadOnlySpan\IndexOf.char.cs" />