Pull_session doesn't work if i don't include 'from bokeh.server.server import Server' statement which i am not using anywhere

@Gopi_M I don’t have an explanation for you, because it makes no sense to me. However, I can reproduce he problem, on Windows only. The example/embed/server_session example works just fine on OSX and Linux, which is probably why this bug has not been noticed before. In any case, please file a bug report on GitHub