NotSupportedException: NuGet does not support /packagesource

[sbrl]

I've just installed omnisharp in atom, and I got this exception:

An unhandled exception has occurred: NuGet does not support /packagesource
System.NotSupportedException: NuGet does not support /packagesource
  at OmniSharp.Middleware.Endpoint.EndpointHandler`2+d__18[TRequest,TResponse].MoveNext () [0x00119] in :0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003e] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in :0 
  at OmniSharp.Middleware.Endpoint.EndpointHandler`2+d__16[TRequest,TResponse].MoveNext () [0x002f3] in :0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003e] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in :0 
  at OmniSharp.Middleware.EndpointMiddleware+d__7.MoveNext () [0x000d8] in :0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003e] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in :0 
  at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in :0 
  at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware+d__6.MoveNext () [0x00080] in <54abb6e5c34d41e5b18eb3ce35092c5b>:0

Incidentally, omnisharp appears to have an issue whereby it doesn't recognise and hint for things in installed nuget packages.

I'm on ubuntu 17.04, and I've also filed #1003.