fix IsSet for string properties

Author: peterrsongg

generator/ServiceModels/s3/s3.customizations.json

@@ -841,6 +841,12 @@
             "modify":[
                 {
                     "Id":{"emitPropertyName": "MetricsId"}
+                },
+                {
+                    "ExpectedBucketOwner" :{"injectXmlIsSet":["return !string.IsNullOrEmpty(this._expectedBucketOwner);"]}
+                },
+                {
+                    "MetricsId":{"injectXmlIsSet":["return !string.IsNullOrEmpty(this._metricsId);"]}
                 }
             ]
         }

sdk/src/Services/S3/Generated/Model/DeleteBucketMetricsConfigurationRequest.cs

@@ -128,7 +128,7 @@ public string ExpectedBucketOwner
         // Check to see if ExpectedBucketOwner property is set
         internal bool IsSetExpectedBucketOwner()
         {
-            return this._expectedBucketOwner != null;
+            return !string.IsNullOrEmpty(this._expectedBucketOwner);
         }
 
         /// <summary>
@@ -148,7 +148,7 @@ public string MetricsId
         // Check to see if MetricsId property is set
         internal bool IsSetMetricsId()
         {
-            return this._metricsId != null;
+            return !string.IsNullOrEmpty(this._metricsId);
         }
 
     }