Add `[NotNullIfNotNull]` to conversions from `string` to `JsonNode`. (#74643)

src/libraries/System.Text.Json/ref/System.Text.Json.cs

@@ -718,6 +718,7 @@ public abstract partial class JsonNode
         [System.CLSCompliantAttribute(false)]
         public static implicit operator System.Text.Json.Nodes.JsonNode (sbyte value) { throw null; }
         public static implicit operator System.Text.Json.Nodes.JsonNode (float value) { throw null; }
+        [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("value")]
         public static implicit operator System.Text.Json.Nodes.JsonNode? (string? value) { throw null; }
         [System.CLSCompliantAttribute(false)]
         public static implicit operator System.Text.Json.Nodes.JsonNode (ushort value) { throw null; }
@@ -799,6 +800,7 @@ public abstract partial class JsonValue : System.Text.Json.Nodes.JsonNode
         [System.CLSCompliantAttribute(false)]
         public static System.Text.Json.Nodes.JsonValue Create(sbyte value, System.Text.Json.Nodes.JsonNodeOptions? options = default(System.Text.Json.Nodes.JsonNodeOptions?)) { throw null; }
         public static System.Text.Json.Nodes.JsonValue Create(float value, System.Text.Json.Nodes.JsonNodeOptions? options = default(System.Text.Json.Nodes.JsonNodeOptions?)) { throw null; }
+        [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("value")]
         public static System.Text.Json.Nodes.JsonValue? Create(string? value, System.Text.Json.Nodes.JsonNodeOptions? options = default(System.Text.Json.Nodes.JsonNodeOptions?)) { throw null; }
         public static System.Text.Json.Nodes.JsonValue? Create(System.Text.Json.JsonElement value, System.Text.Json.Nodes.JsonNodeOptions? options = default(System.Text.Json.Nodes.JsonNodeOptions?)) { throw null; }
         [System.CLSCompliantAttribute(false)]

src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonNode.Operators.cs

 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace System.Text.Json.Nodes
 {
     public partial class JsonNode
@@ -194,6 +196,7 @@ public partial class JsonNode
         /// </summary>
         /// <param name="value">A <see cref="string"/> to implicitly convert.</param>
         /// <returns>A <see cref="JsonNode"/> instance converted from the <paramref name="value"/> parameter.</returns>
+        [return: NotNullIfNotNull(nameof(value))]
         public static implicit operator JsonNode?(string? value) => JsonValue.Create(value);
 
         /// <summary>

src/libraries/System.Text.Json/src/System/Text/Json/Nodes/JsonValue.CreateOverloads.cs

 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Text.Json.Serialization.Metadata;
 
 namespace System.Text.Json.Nodes
@@ -223,6 +224,7 @@ public partial class JsonValue
         /// <param name="value">The underlying value of the new <see cref="JsonValue"/> instance.</param>
         /// <param name="options">Options to control the behavior.</param>
         /// <returns>The new instance of the <see cref="JsonValue"/> class that contains the specified value.</returns>
+        [return: NotNullIfNotNull(nameof(value))]
         public static JsonValue? Create(string? value, JsonNodeOptions? options = null) => value != null ? new JsonValueTrimmable<string>(value, JsonMetadataServices.StringConverter) : null;
 
         /// <summary>