Java enum template needs to include SerializableName for each member
https://github.com/microsoftgraph/MSGraph-SDK-Code-Generator/blob/dev/Templates/Java/models_generated/Enum.java.tt

```java
public void testGetMailtips() {
		TestBase testBase = new TestBase();
		ArrayList<String> users = new ArrayList<String>();
		users.add("michael@chambele.onmicrosoft.com");
		users.add("AdeleV@chambele.onmicrosoft.com");
		EnumSet<MailTipsType> mailtips = EnumSet.of(MailTipsType.MAILBOX_FULL_STATUS, MailTipsType.MAX_MESSAGE_SIZE);
		UserGetMailTipsCollectionPage page = testBase.graphClient.me().getMailTips(users, mailtips).buildRequest().post();
		assertNotNull(page);
	}
```
results in the following body:
```json
{
    "emailAddresses": ["michael@chambele.onmicrosoft.com", "AdeleV@chambele.onmicrosoft.com"],
    "mailTipsOptions": "MAILBOX_FULL_STATUS,MAX_MESSAGE_SIZE"
}
```
expected:
```json
{
    "emailAddresses": ["michael@chambele.onmicrosoft.com", "AdeleV@chambele.onmicrosoft.com"],
    "mailTipsOptions": "mailboxFullStatus,maxMessageSize"
}
```
diff --git a/src/main/java/com/microsoft/graph/serializer/EnumSetSerializer.java b/src/main/java/com/microsoft/graph/serializer/EnumSetSerializer.java
index b7ee710748..daf345c531 100644
--- a/src/main/java/com/microsoft/graph/serializer/EnumSetSerializer.java
+++ b/src/main/java/com/microsoft/graph/serializer/EnumSetSerializer.java
@@ -22,7 +22,9 @@
 package com.microsoft.graph.serializer;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import com.google.gson.JsonPrimitive;
+import com.microsoft.graph.logger.ILogger;
 
 import java.lang.reflect.Type;
 import java.util.EnumSet;
@@ -36,39 +38,43 @@ import java.util.Iterator;
  */
 public class EnumSetSerializer {
 
+    private final Gson gson;
     /**
      * Not available for instantiation
      */
-    private EnumSetSerializer() {
+    public EnumSetSerializer(final ILogger logger) {
+         gson = new GsonBuilder().registerTypeAdapterFactory(new FallbackTypeAdapterFactory(logger)).create();
     }
 
     /**
      * Deserializes a comma-delimited string of enum values
-     * 
+     *
      * @param type                 the type
      * @param jsonStrToDeserialize the string to deserialize
      * @return                     EnumSet of values
      */
-    public static EnumSet<?> deserialize(Type type, String jsonStrToDeserialize) {
-            Gson gson = new Gson();
-            String arrayString = "[" + jsonStrToDeserialize + "]";
+    public EnumSet<?> deserialize(Type type, String jsonStrToDeserialize) {
+            final String arrayString = "[" + jsonStrToDeserialize + "]";
             return jsonStrToDeserialize == null ? null : (EnumSet<?>) gson.fromJson(arrayString, type);
     }
 
     /**
      * Serializes an EnumSet into a comma-delimited string
-     * 
+     *
      * @param src the source EnumSet
      * @return    a comma-delimited string of enum values
      */
-    public static JsonPrimitive serialize(EnumSet<?> src) {
-        String serializedString = "";
+    public JsonPrimitive serialize(EnumSet<?> src) {
+        final StringBuilder serializedStringBuilder = new StringBuilder();
 
-        Iterator<?> i = src.iterator();
+        final Iterator<?> i = src.iterator();
         while (i.hasNext()) {
-            serializedString += i.next().toString() + ",";
+            final String jsonValue = gson.toJson(i.next());
+            serializedStringBuilder.append(jsonValue.substring(1, jsonValue.length() -1));
+            if(i.hasNext()) {
+                serializedStringBuilder.append(",");
+            }
         }
-        serializedString = serializedString.substring(0, serializedString.length()-1);
-        return new JsonPrimitive(serializedString);
+        return new JsonPrimitive(serializedStringBuilder.toString());
     }
 }
diff --git a/src/main/java/com/microsoft/graph/serializer/GsonFactory.java b/src/main/java/com/microsoft/graph/serializer/GsonFactory.java
index 02c433ad2b..746825efbd 100644
--- a/src/main/java/com/microsoft/graph/serializer/GsonFactory.java
+++ b/src/main/java/com/microsoft/graph/serializer/GsonFactory.java
@@ -51,7 +51,7 @@ import javax.xml.datatype.Duration;
 final class GsonFactory {
 
 	private static String PARSING_MESSAGE = "Parsing issue on ";
-	
+
     /**
      * Default constructor
      */
@@ -163,6 +163,7 @@ final class GsonFactory {
                 }
             }
         };
+        final EnumSetSerializer eSetSerializer = new EnumSetSerializer(logger);
 
         final JsonSerializer<EnumSet<?>> enumSetJsonSerializer = new JsonSerializer<EnumSet<?>>() {
             @Override
@@ -173,7 +174,7 @@ final class GsonFactory {
                     return null;
                 }
 
-                return EnumSetSerializer.serialize(src);
+                return eSetSerializer.serialize(src);
             }
         };
 
@@ -186,7 +187,7 @@ final class GsonFactory {
                     return null;
                 }
 
-                return EnumSetSerializer.deserialize(typeOfT, json.getAsString());
+                return eSetSerializer.deserialize(typeOfT, json.getAsString());
             }
         };
 
@@ -211,7 +212,7 @@ final class GsonFactory {
                 }
             }
         };
-        
+
         final JsonSerializer<BaseCollectionPage<?,?>> collectionPageSerializer = new JsonSerializer<BaseCollectionPage<?,?>>() {
             @Override
             public JsonElement serialize(final BaseCollectionPage<?,?> src,
@@ -229,7 +230,7 @@ final class GsonFactory {
                 return CollectionPageSerializer.deserialize(json, typeOfT, logger);
             }
         };
-        
+
         final JsonDeserializer<TimeOfDay> timeOfDayJsonDeserializer = new JsonDeserializer<TimeOfDay>() {
             @Override
             public TimeOfDay deserialize(final JsonElement json,
diff --git a/src/test/java/com/microsoft/graph/serializer/DefaultSerializerTests.java b/src/test/java/com/microsoft/graph/serializer/DefaultSerializerTests.java
index bcd63ef043..5ffaff18a8 100644
--- a/src/test/java/com/microsoft/graph/serializer/DefaultSerializerTests.java
+++ b/src/test/java/com/microsoft/graph/serializer/DefaultSerializerTests.java
@@ -4,11 +4,17 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.EnumSet;
+
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import com.google.gson.annotations.Expose;
 import com.google.gson.annotations.SerializedName;
 import com.microsoft.graph.callrecords.models.extensions.MediaStream;
+import com.microsoft.graph.functional.TestBase;
+import com.microsoft.graph.http.HttpMethod;
 import com.microsoft.graph.http.MockConnection;
 import com.microsoft.graph.logger.DefaultLogger;
 import com.microsoft.graph.models.extensions.Attachment;
@@ -17,11 +23,18 @@ import com.microsoft.graph.models.extensions.Drive;
 import com.microsoft.graph.models.extensions.FileAttachment;
 import com.microsoft.graph.models.extensions.RecurrenceRange;
 import com.microsoft.graph.models.extensions.User;
+import com.microsoft.graph.models.extensions.UserGetMailTipsBody;
+import com.microsoft.graph.models.generated.MailTipsType;
 import com.microsoft.graph.models.generated.RecurrenceRangeType;
 import com.microsoft.graph.requests.extensions.DriveItemDeltaCollectionResponse;
 import com.microsoft.graph.models.extensions.UploadSession;
+
+import org.junit.Assert;
 import org.junit.Test;
 
+import okhttp3.Request;
+import okio.Buffer;
+
 public class DefaultSerializerTests {
 
 	/**
@@ -111,19 +124,19 @@ public class DefaultSerializerTests {
         assertNotNull(jsonOut);
         assertEquals(expected, jsonOut);
     }
-	
+
 	@Test
 	public void testResponseHeaders() throws Exception {
 		MockConnection connection = new MockConnection(null);
 		final DefaultSerializer serializer = new DefaultSerializer(new DefaultLogger());
 		User user = serializer.deserializeObject("{\\"id\\":\\"1\\"}", User.class, connection.getResponseHeaders());
-		
+
 		JsonElement responseHeaders = user.additionalDataManager().get("graphResponseHeaders");
 		assertNotNull(responseHeaders);
-		
+
 		JsonElement responseHeader = responseHeaders.getAsJsonObject().get("header1");
 		assertNotNull(responseHeader);
-		
+
 		assertEquals("value1", responseHeader.getAsJsonArray().get(0).getAsString());
 	}
 
@@ -132,25 +145,25 @@ public class DefaultSerializerTests {
 		final DefaultSerializer serializer = new DefaultSerializer(new DefaultLogger());
 		final String source = "{\\"@odata.context\\": \\"/attachments/$entity\\",\\"@odata.type\\": \\"#microsoft.graph.fileAttachment\\",\\"id\\": \\"AAMkAGQ0MjBmNWVkLTYxZjUtNDRmYi05Y2NiLTBlYjIwNzJjNmM1NgBGAAAAAAC6ff7latYeQqu_gLrhSAIhBwCF7iGjpaOmRqVwbZc-xXzwAAAAAAEMAACF7iGjpaOmRqVwbZc-xXzwAABQStA0AAABEgAQAFbGmeisbjtLnQdp7kC_9Fk=\\",\\"lastModifiedDateTime\\": \\"2018-01-23T21:50:22Z\\",\\"name\\": \\"Test Book.xlsx\\",\\"contentType\\": \\"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet\\",\\"size\\": 8457,\\"isInline\\": false,\\"contentId\\": null,\\"contentLocation\\": null,\\"contentBytes\\": \\"bytedata\\"}";
 		final Attachment result = serializer.deserializeObject(source, Attachment.class);
-		
+
 		assert(result instanceof FileAttachment);
-		
+
 		final FileAttachment fileAttachment = (FileAttachment) result;
 		assertNotNull(fileAttachment.contentBytes);
 		final JsonObject o = fileAttachment.getRawObject();
 		assertNotNull(o);
 		assertEquals("#microsoft.graph.fileAttachment", o. get("@odata.type").getAsString());
 	}
-  
+
     @Test
     public void testSerializerCanSerializeVoidWithoutEmittingWarning() {
         // Unfortunately does not assert for existence of Java 9 illegal access warnings
-        // which seem to written to the console without use of System.err/System.out (so cannot be captured AFAIK). 
+        // which seem to written to the console without use of System.err/System.out (so cannot be captured AFAIK).
         // @davidmoten
         final DefaultSerializer serializer = new DefaultSerializer(new DefaultLogger());
         HasVoidMember t = new HasVoidMember();
         String json = serializer.serializeObject(t);
-        // this line will emit a warning from Java 9 about illegal access to the constructor of Void 
+        // this line will emit a warning from Java 9 about illegal access to the constructor of Void
         // if gson TypeAdapterFactory is not handling Void properly
         HasVoidMember t2 = serializer.deserializeObject(json, HasVoidMember.class);
         assertEquals(t.x, t2.x);
@@ -173,12 +186,28 @@ public class DefaultSerializerTests {
         assertNotNull(result);
         assertNotNull(result.maxRoundTripTime);
     }
-  
+    @Test
+    public void testEnumActionParameterDeserialization() throws IOException {
+        final ArrayList<String> users = new ArrayList<String>();
+        users.add("michael@chambele.onmicrosoft.com");
+        final EnumSet<MailTipsType> mailtips = EnumSet.of(MailTipsType.MAILBOX_FULL_STATUS, MailTipsType.MAX_MESSAGE_SIZE);
+        final UserGetMailTipsBody body = new UserGetMailTipsBody();
+        body.emailAddresses = users;
+        body.mailTipsOptions = mailtips;
+        final DefaultSerializer serializer = new DefaultSerializer(new DefaultLogger());
+        final String serialized = serializer.serializeObject(body);
+        Assert.assertTrue("result contains camelCasedValues", serialized.contains("mailboxFullStatus"));
+
+        final UserGetMailTipsBody deserialized = serializer.deserializeObject(serialized, UserGetMailTipsBody.class);
+
+        Assert.assertEquals(2, deserialized.mailTipsOptions.size());
+    }
+
   public static final class HasVoidMember {
       @SerializedName("x")
       @Expose
       int x = 1;
-      
+
       @SerializedName("y")
       @Expose
       Void y;
['src/main/java/com/microsoft/graph/serializer/EnumSetSerializer.java', 'src/test/java/com/microsoft/graph/serializer/DefaultSerializerTests.java', 'src/main/java/com/microsoft/graph/serializer/GsonFactory.java']