HttpClient errors in log

[Raa007]

When using HTC One M9 phone to play MP3 files from server, constantly get HttpClient messages in log.

Extract of some of these messages are:
2016-01-10 13:09:23,537 INFO [ 7] HttpClient - 192.168.10.11:39376 - 500 response for /mm-1/cover/3E9EDA83/i.jpg
2016-01-10 13:09:23,662 INFO [ 12] MediaMount - Serving cover 3E9EDA83
2016-01-10 13:09:23,662 WARN [ 12] HttpClient - 192.168.10.11:48154 - Failed to process response
System.NullReferenceException: Object reference not set to an instance of an object.
at NMaier.SimpleDlna.Server.ItemResponse..ctor(String prefix, IRequest request, IMediaResource item, String transferMode)
at NMaier.SimpleDlna.Server.MediaMount.HandleRequest(IRequest request)
at NMaier.SimpleDlna.Server.HttpClient.SetupResponse()
2016-01-10 13:09:23,662 INFO [ 12] HttpClient - 192.168.10.11:48154 - 500 response for /mm-1/cover/3E9EDA83/i.jpg
2016-01-10 13:09:23,662 INFO [ 11] MediaMount - Serving cover 35FFBAD3
2016-01-10 13:09:23,662 WARN [ 11] HttpClient - 192.168.10.11:60287 - Failed to process response
System.NullReferenceException: Object reference not set to an instance of an object.
at NMaier.SimpleDlna.Server.ItemResponse..ctor(String prefix, IRequest request, IMediaResource item, String transferMode)
at NMaier.SimpleDlna.Server.MediaMount.HandleRequest(IRequest request)
at NMaier.SimpleDlna.Server.HttpClient.SetupResponse()
2016-01-10 13:09:23,662 INFO [ 11] HttpClient - 192.168.10.11:60287 - 500 response for /mm-1/cover/35FFBAD3/i.jpg
2016-01-10 13:09:23,662 INFO [ 13] MediaMount - Serving cover 14724884
2016-01-10 13:09:23,662 WARN [ 13] HttpClient - 192.168.10.11:59837 - Failed to process response
System.NullReferenceException: Object reference not set to an instance of an object.
at NMaier.SimpleDlna.Server.ItemResponse..ctor(String prefix, IRequest request, IMediaResource item, String transferMode)
at NMaier.SimpleDlna.Server.MediaMount.HandleRequest(IRequest request)
at NMaier.SimpleDlna.Server.HttpClient.SetupResponse()
2016-01-10 13:09:23,662 INFO [ 13] HttpClient - 192.168.10.11:59837 - 500 response for /mm-1/cover/14724884/i.jpg
2016-01-10 13:09:24,239 INFO [ 8] MediaMount - Serving cover 0F9C1133
2016-01-10 13:09:24,239 WARN [ 8] HttpClient