Compare updated template evaluator (#4092)

src/Sdk/Expressions/Data/StringExpressionData.cs

@@ -0,0 +1,74 @@
+#nullable disable // Consider removing in the future to minimize likelihood of NullReferenceException; refer https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references
+
+using System;
+using System.Runtime.Serialization;
+using GitHub.Actions.Expressions.Sdk;
+using Newtonsoft.Json.Linq;
+
+namespace GitHub.Actions.Expressions.Data
+{
+    [DataContract]
+    public sealed class StringExpressionData : ExpressionData, IString
+    {
+        public StringExpressionData(String value)
+            : base(ExpressionDataType.String)
+        {
+            m_value = value;
+        }
+
+        public String Value
+        {
+            get
+            {
+                if (m_value == null)
+                {
+                    m_value = String.Empty;
+                }
+
+                return m_value;
+            }
+        }
+
+        public override ExpressionData Clone()
+        {
+            return new StringExpressionData(m_value);
+        }
+
+        public override JToken ToJToken()
+        {
+            return (JToken)m_value;
+        }
+
+        String IString.GetString()
+        {
+            return Value;
+        }
+
+        public override String ToString()
+        {
+            return Value;
+        }
+
+        public static implicit operator String(StringExpressionData data)
+        {
+            return data.Value;
+        }
+
+        public static implicit operator StringExpressionData(String data)
+        {
+            return new StringExpressionData(data);
+        }
+
+        [OnSerializing]
+        private void OnSerializing(StreamingContext context)
+        {
+            if (m_value?.Length == 0)
+            {
+                m_value = null;
+            }
+        }
+
+        [DataMember(Name = "s", EmitDefaultValue = false)]
+        private String m_value;
+    }
+}