/// <summary>
 /// Looks up the specified key in the <see cref="MDC"/>.
 /// </summary>
 /// <param name="key">The key to lookup.</param>
 /// <returns>
 /// The value associated with the key, or <c>null</c> if the key was not found.
 /// </returns>
 public string LookupMappedContext(string key)
 {
     if (m_data.MDC == null)
     {
         // This creates a live copy of the MDC
         m_data.MDC = MDC.GetMap();
     }
     return(m_data.MDC[key] as string);
 }