message: Remove empty body from GET requests
  Spotify rejects GET requests that have a body with a 400 response
  code.
diff: @@ -94,7 +94,7 @@ impl Spotify {
  }
  }
  - fn internal_call(&self, method: Method, url: &str, payload: &Value) -> Result<String> {
  + fn internal_call(&self, method: Method, url: &str, payload: Option<&Value>) -> Result<String> {
  let mut url: Cow<str> = url.into();
  if !url.starts_with("http") {
  url = ["https://api.spotify.com/v1/", &url].concat().into();
  @@ -103,12 +103,19 @@ impl Spotify {
  let mut headers = Headers::new();
  headers.set(self.auth_headers());
  headers.set(ContentType::json());
  - let mut response = CLIENT
  - .request(method, &url.into_owned())
  - .headers(headers)
  - .json(&payload)
  - .send()
  - .expect("send request failed");
  +
  + let mut response = {
  + let mut builder = CLIENT.request(method, &url.into_owned());
  + builder.headers(headers);
  +
  + // only add body if necessary
  + // spotify rejects GET requests that have a body with a 400 response
  + if let Some(json) = payload {
  + builder.json(json);
  + }
  +
  + builder.send().unwrap()
  + };
  let mut buf = String::new();
  response
  @@ -132,24 +139,24 @@ impl Spotify {
  let mut url_with_params = url.to_owned();
  url_with_params.push('?');
  url_with_params.push_str(&param);
  - self.internal_call(Get, &url_with_params, &json!({}))
  + self.internal_call(Get, &url_with_params, None)
  } else {
  - self.internal_call(Get, url, &json!({}))
  + self.internal_call(Get, url, None)
  }
  }
  ///send post request
  fn post(&self, url: &str, payload: &Value) -> Result<String> {
  - self.internal_call(Post, url, payload)
  + self.internal_call(Post, url, Some(payload))
  }
  ///send put request
  fn put(&self, url: &str, payload: &Value) -> Result<String> {
  - self.internal_call(Put, url, payload)
  + self.internal_call(Put, url, Some(payload))
  }
  /// send delete request
  fn delete(&self, url: &str, payload: &Value) -> Result<String> {
  - self.internal_call(Delete, url, payload)
  + self.internal_call(Delete, url, Some(payload))
  }
  ///[get-track](https://developer.spotify.com/web-api/get-track/)
  