Fixed Javadoc in callback helper, add additional checks for emptiness in internal/utility helper

Author: nightowlengineer

src/main/java/engineer/nightowl/sonos/api/util/SonosCallbackHelper.java

@@ -23,7 +23,9 @@ public class SonosCallbackHelper
     /**
      * Verify that the message was signed by Sonos.
      *
-     * @param headers from the message
+     * @param headers   from the message
+     * @param apiKey    of your integration
+     * @param apiSecret of your integration
      * @return true if the message is cryptographically provable to be from Sonos
      * @throws SonosApiClientException if in an unsupported environment
      */

src/main/java/engineer/nightowl/sonos/api/util/SonosUtilityHelper.java

@@ -38,13 +38,25 @@ public static boolean isEmpty(final Map<?, ?> map)
     }
 
     /**
-     * This method returns true if the objet is null.
+     * This method returns true if the object is null.
      *
      * @param object to check if null
      * @return true | false
      */
     public static boolean isEmpty(final Object object)
     {
+        if (object instanceof Map)
+        {
+            return isEmpty((Map) object);
+        }
+        if (object instanceof String)
+        {
+            return isEmpty((String) object);
+        }
+        if (object instanceof Collection)
+        {
+            return isEmpty((Collection) object);
+        }
         if (object == null)
         {
             return true;