Fix DynamoDB tests

sdk/src/Core/Amazon.Runtime/Internal/Endpoints/StandardLibrary/Fn.cs

@@ -367,6 +367,8 @@ public static string Interpolate(string template, Dictionary<string, object> ref
         /// </summary>
         public static string InterpolateJson(string json, Dictionary<string, object> refs)
         {
+            if (string.IsNullOrEmpty(json))
+                return string.Empty;
             try
             {
                 using JsonDocument doc = JsonDocument.Parse(json);
@@ -381,7 +383,7 @@ public static string InterpolateJson(string json, Dictionary<string, object> ref
             }
             catch (JsonException)
             {
-                return "";
+                return string.Empty;
             }
         }
 

sdk/src/Services/DynamoDBv2/Custom/AWSConfigs.DynamoDB.cs

@@ -57,6 +57,11 @@ static AWSConfigsDynamoDB()
 
         #region DynamoDBContext TableNamePrefix
 
+        /// <summary>
+        /// Key for the DynamoDBContextTableNamePrefix property.
+        /// </summary>
+        public const string DynamoDBContextTableNamePrefixKey = "AWS.DynamoDBContext.TableNamePrefix";
+
         #endregion
 
         /// <summary>
@@ -171,7 +176,7 @@ public void AddMapping(TypeMapping typeMapping)
 
         internal DynamoDBContextConfig()
         {
-            this.TableNamePrefix = AWSConfigs.GetConfig(AWSConfigsDynamoDB.Context.TableNamePrefix);
+            this.TableNamePrefix = AWSConfigs.GetConfig(AWSConfigsDynamoDB.DynamoDBContextTableNamePrefixKey);
 
             TableAliases = new Dictionary<string, string>(StringComparer.Ordinal);
             TypeMappings = new Dictionary<Type, TypeMapping>();