fixes a bug where timeofday would not be serialized properly

src/main/java/com/microsoft/graph/serializer/GsonFactory.java

@@ -256,6 +256,15 @@ public TimeOfDay deserialize(final JsonElement json,
             }
         };
 
+        final JsonSerializer<TimeOfDay> timeOfDayJsonSerializer = new JsonSerializer<TimeOfDay>() {
+            @Override
+            public JsonElement serialize(final TimeOfDay src,
+                                         final Type typeOfSrc,
+                                         final JsonSerializationContext context) {
+                return new JsonPrimitive(src.toString());
+            }
+        };
+
         final JsonDeserializer<Boolean> booleanJsonDeserializer = new JsonDeserializer<Boolean>() {
             @Override
             public Boolean deserialize(final JsonElement json,
@@ -344,6 +353,7 @@ public Float deserialize(final JsonElement json,
                 .registerTypeHierarchyAdapter(BaseCollectionPage.class, collectionPageDeserializer)
                 .registerTypeHierarchyAdapter(BaseCollectionResponse.class, collectionResponseDeserializer)
                 .registerTypeAdapter(TimeOfDay.class, timeOfDayJsonDeserializer)
+                .registerTypeAdapter(TimeOfDay.class, timeOfDayJsonSerializer)
                 .registerTypeAdapterFactory(new FallbackTypeAdapterFactory(logger))
                 .create();
     }

src/test/java/com/microsoft/graph/serializer/TimeOfDayTests.java

@@ -1,10 +1,12 @@
 package com.microsoft.graph.serializer;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
 
 import org.junit.jupiter.api.Test;
 
 import com.microsoft.graph.core.TimeOfDay;
+import com.microsoft.graph.logger.ILogger;
 
 public class TimeOfDayTests {
 
@@ -43,5 +45,11 @@ public void testTimeOfDayDeserializerWithFraction() throws Exception{
         assertEquals(30, time.getMinute());
         assertEquals(44, time.getSecond());
     }
-
+    @Test
+    public void testTimeOfDaySerialization() throws Exception {
+        final TimeOfDay time = new TimeOfDay(12, 30, 44);
+        final ILogger logger = mock(ILogger.class);
+        final ISerializer serializer = new DefaultSerializer(logger);
+        assertEquals("\"12:30:44\"", serializer.serializeObject(time));
+    }
 }