ctx.readAsJson() error "Bad state: Stream has already been listened to."

[vvnab]

app.post("/todos", (HttpContext ctx){
ctx.readAsJson().then((x){
ctx.sendJson(x);
});
})

don`t work
trow error
"""
Bad state: Stream has already been listened to.

StackTrace:
#0 _StreamController._subscribe (dart:async/stream_controller.dart:601)
#1 _ControllerStream._createSubscription (dart:async/stream_controller.dart:790)
#2 _StreamImpl.listen (dart:async/stream_impl.dart:474)
#3 _ForwardingStreamSubscription._ForwardingStreamSubscription (dart:async/stream_pipe.dart:129)
#4 _ForwardingStream._createSubscription (dart:async/stream_pipe.dart:96)
#5 _ForwardingStream.listen (dart:async/stream_pipe.dart:88)
#6 _HttpIncoming.listen (dart:io/http_impl.dart:47)
#7 _HttpRequest.listen (dart:io/http_impl.dart:119)
#8 _SinkTransformerStreamSubscription._SinkTransformerStreamSubscription (dart:async/stream_transformers.dart:46)
#9 _BoundSinkStream.listen (dart:async/stream_transformers.dart:186)
#10 _HttpContext.readAsText (package:express/_http_context.dart:85:14)
#11 _HttpContext.readAsJson (package:express/_http_context.dart:95:17)
#12 main.

"""