issue wrapping async call inside Signal

[tomerciucran]

I am wrapping my network requests into signals like this:

func request<Response>(_ endpoint: Endpoint<Response>) -> Signal<Response, ResponseError> {
        return Signal<Response, ResponseError> { observer in
            let request = self.manager.request(
                self.url(path: endpoint.path),
                method: httpMethod(from: endpoint.method),
                parameters: endpoint.parameters,
                encoding: endpoint.encoding
            )
            request
                .validate()
                .responseData() { response in
                    let result = response.result.flatMap(endpoint.decode)
                    switch result {
                    case .success(let value):
                        observer.next(value)
                        observer.completed()
                    case .failure(let error):
                        observer.failed(ResponseError(reason: error.localizedDescription,
                                                      statusCode: response.response?.statusCode ?? 0))
                    }
            }
            return BlockDisposable {
                request.cancel()
            }
        }
    }

The issue I am having is that when I am observing this signal, the callback is triggered twice .next with value and .completed. I don't want it to be called twice because obviously I am executing code to update the UI inside the callback.
Sometimes the value is null (for some requests I expect 200 with empty response), so I cannot check the value.
If I don't call .completed after .next, the issue disappears but I not sure if it would cause a memory issue because the signal is being disposed in the case of a .failed or .completed event as seen here:

public func on(_ event: Event<Element, Error>) {
    lock.lock(); defer { lock.unlock() }
    guard !disposable.isDisposed else { return }
    if let observer = observer {
      observer(event)
      if event.isTerminal {
        disposable.dispose()
      }
    }
  } 

Any suggestions?