Changes made to address comments'

Microsoft.Azure.Cosmos/src/Patch/PatchOperation.cs

@@ -29,7 +29,7 @@ public abstract class PatchOperation
         /// Source location reference (used in case of move)
         /// </summary>
         [JsonProperty(PropertyName = PatchConstants.PropertyNames.From)]
-        public abstract string From { get; }
+        public virtual string From { get; set; } = null;
 
         /// <summary>
         /// Serializes the value parameter, if specified for the PatchOperation.
@@ -140,16 +140,16 @@ public static PatchOperation Increment(
                 path,
                 value);
         }
-        
+
         /// <summary>
         /// Create <see cref="PatchOperation"/> to move an object/value.
         /// </summary>
-        /// <param name="path">Target location reference.</param>
         /// <param name="from">The source location of the object/value.</param>
+        /// <param name="path">Target location reference.</param>
         /// <returns>PatchOperation instance for specified input.</returns>
         public static PatchOperation Move(
-            string path,
-            string from)
+            string from,
+            string path)
         {
             return new PatchOperationCore<string>(
                 PatchOperationType.Move,

Microsoft.Azure.Cosmos/src/Patch/PatchOperationCore.cs

@@ -26,6 +26,5 @@ public PatchOperationCore(
         public override PatchOperationType OperationType { get; }
 
         public override string Path { get; }
-        public override string From { get; }
     }
 }

Microsoft.Azure.Cosmos/src/Patch/PatchOperationCore{T}.cs

@@ -10,45 +10,46 @@ namespace Microsoft.Azure.Cosmos
     internal sealed class PatchOperationCore<T> : PatchOperation<T>
     {
         /// <summary>
-        /// Initializes a new instance of the <see cref="PatchOperationCore{T}"/> class.
-        /// </summary>
-        /// <param name="operationType">Specifies the type of Patch operation.</param>
-        /// <param name="path">Specifies the path to target location.</param>
-        /// <param name="value">Specifies the value to be used. In case of move operations it will be a string specifying the source
-        /// location.</param>
+        /// Initializes a new instance of the <see cref="PatchOperationCore{T}"/> class.
+        /// </summary>
+        /// <param name="operationType">Specifies the type of Patch operation.</param>
+        /// <param name="path">Specifies the path to target location.</param>
+        /// <param name="value">Specifies the value to be used. In case of move operations it will be a string specifying the source
+        /// location.</param>
         public PatchOperationCore(
-            PatchOperationType operationType,
-            string path,
-            T value)
+          PatchOperationType operationType,
+          string path,
+          T value)
         {
             this.OperationType = operationType;
             if (operationType == PatchOperationType.Move)
             {
                 this.Path = string.IsNullOrWhiteSpace(path)
                     ? throw new ArgumentNullException(nameof(path))
                     : path;
-
-                this.From = string.IsNullOrWhiteSpace(value.ToString())
+                if (!(value is String valueAsString))
+                {
+                    throw new ArgumentException(
+                    $"Parameter {nameof(value)} must be of type String for patch operation type {nameof(PatchOperationType.Move)}");
+                }
+                this.From = string.IsNullOrWhiteSpace(valueAsString)
                     ? throw new ArgumentNullException(nameof(value))
-                    : value.ToString();
+                    : valueAsString;
             }
             else
             {
                 this.Path = string.IsNullOrWhiteSpace(path)
                     ? throw new ArgumentNullException(nameof(path))
                     : path;
-                this.Value = value; 
+                this.Value = value;
             }
         }
-
         public override T Value { get; }
 
         public override PatchOperationType OperationType { get; }
 
         public override string Path { get; }
 
-        public override string From { get; }
-
         public override bool TrySerializeValueParameter(
             CosmosSerializer cosmosSerializer,
             out Stream valueParam)

Microsoft.Azure.Cosmos/src/Patch/PatchOperationsJsonConverter.cs

@@ -93,8 +93,7 @@ public override void WriteJson(
                     writer.WritePropertyName(PatchConstants.PropertyNames.From);
                     writer.WriteValue(operation.From);
                 }
-
-                if (operation.TrySerializeValueParameter(this.userSerializer, out Stream valueStream))
+                else if (operation.TrySerializeValueParameter(this.userSerializer, out Stream valueStream))
                 {
                     string valueParam;
                     using (valueStream)

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/Batch/BatchSinglePartitionKeyTests.cs

@@ -694,7 +694,7 @@ public async Task BatchCustomSerializerUsedForPatchAsync()
             List<PatchOperation> patchOperations = new List<PatchOperation>()
             {
                 PatchOperation.Add("/date", patchDate),
-                PatchOperation.Move("/TodayDate", "/date")
+                PatchOperation.Move("/date", "/TodayDate")
             };
 
             BatchCore batch = (BatchCore)new BatchCore((ContainerInlineCore)customSerializationContainer, BatchTestBase.GetPartitionKey(this.PartitionKey1))

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/CosmosItemTests.cs

@@ -2004,8 +2004,8 @@ public async Task ItemPatchSuccessTest()
 
             patchOperations.Clear();
             patchOperations.Add(PatchOperation.Add("/children/1/description","Child#1"));
-            patchOperations.Add(PatchOperation.Move("/description", "/children/0/description"));
-            patchOperations.Add(PatchOperation.Move("/children/0/description", "/children/1/description"));
+            patchOperations.Add(PatchOperation.Move("/children/0/description", "/description"));
+            patchOperations.Add(PatchOperation.Move("/children/1/description", "/children/0/description"));
             // with content response
             response = await containerInternal.PatchItemAsync<ToDoActivity>(
                 id: testItem.id,