Update documentation to describe how to avoid Java.Lang.NullPointerException

[masesdevelopers]

If the hypothesis is correct, to avoid the GC retires the object, we try to execute the following code:

            try
            {
                GC.SuppressFinalize(kRecord);
                return Send(kRecord);
            }
            finally { GC.ReRegisterForFinalize(kRecord); }

Originally posted by @masesdevelopers in masesgroup/KNet#242 (comment)