iOS SetRenderTarget(null) crashes

Hello,
in my project, where there is a Windows and an iOS version, there is a drawing method that looks like this:

private void RenderRouteToTexture()
{
GraphicsDevice.SetRenderTarget(_routeRenderTarget);
[…]
GraphicsDevice.SetRenderTarget(null);
}

This works perfectly fine with Windows, but for some reason, it crashes when reaching the “SetRenderTarget(null)” part when executed by the iOS version, throwing a System.NullReferenceException without any details other than the usual “Object reference not set to an instance of an object.”.
Is this a known issue and if so, is there another way to reset the render target to the back buffer?

Regards,
Dokug