using System;

using System.Linq;

using System.Collections.Generic;                   

public class Program

{

    public class DeviceConfiguration

    {

        public string ContentTree { get; set; }

    }

    public class DeviceConnection

    {

        /// <summary>

        /// SignalR ConnectionId

        /// </summary>

        public string ConnectionId { get; set; }

​

        /// <summary>

        /// Device configuration from the Hospital Service

        /// </summary>

        public DeviceConfiguration DeviceConfiguration { get; set; }

    }

    public static void Main()

    {

        IEnumerable<DeviceConnection> nonNullIEnumerable = new List<DeviceConnection> 

        {

            new DeviceConnection { ConnectionId = "a", DeviceConfiguration = null},

            new DeviceConnection { ConnectionId = "b", DeviceConfiguration = new DeviceConfiguration {ContentTree = "ct"}},     

            new DeviceConnection { ConnectionId = "c", DeviceConfiguration = null},

        };

        if (nonNullIEnumerable != null && nonNullIEnumerable.Any())

        {

            var result = nonNullIEnumerable.Where(x => x.DeviceConfiguration == null).ToList();

            Console.Write(string.Join(",\n",result.Select(x => x.ConnectionId)));

        }

        else

            Console.Write("empty or null");

    }

}