Unable to modify request body

Hi, I am trying to write a custom plugin to expose a SOAP Web Service as REST API.

I read the docs and I managed to convert from json to correct SOAP request, but when it comes to send the request to the target service I get this error

{"message":"write after end","code":"ERR_STREAM_WRITE_AFTER_END"}

To be sure that it was not my plugin's fault, I tried with a fresh installation (I'm using latest version 3.1.4 on a docker container), with only one plugin activated: accumulate-request. I configured httpbin.org as target service, so I can inspect what flows out from MG.

When I send a POST request with no body, everything works as expected and httpbin respond correctly, but as I try to put something in the body I get the same error as above (here with the full stack trace):

2020-06-19T13:25:49.439Z gateway:main targetRequest error 64038cb0-b230-11ea-b7ce-4582586cfc80 Error [ERR_STREAM_WRITE_AFTER_END]: write after end
at write_ (_http_outgoing.js:637:17)
at ClientRequest.write (_http_outgoing.js:629:15)
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/lib/plugins-middleware.js:434:35
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:1154:26
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:380:13
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:52:16
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:269:32
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:44:16
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:377:17
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:1150:21
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:167:37
at fx (/usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/lib/plugins-middleware.js:579:25)
at onend_request (/usr/local/lib/node_modules/edgemicro/node_modules/microgateway-plugins/accumulate-request/index.js:36:7)
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/lib/plugins-middleware.js:596:31
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:1149:20
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:375:13
2020-06-19T13:25:49.439Z gateway:main plugin analytics does not provide handler function for error_request
2020-06-19T13:25:49.439Z gateway:main plugin accumulate-request does not provide handler function for error_request
2020-06-19T13:25:49.440Z gateway:errors Error [ERR_STREAM_WRITE_AFTER_END]: write after end
at write_ (_http_outgoing.js:637:17)
at ClientRequest.write (_http_outgoing.js:629:15)
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/lib/plugins-middleware.js:434:35
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:1154:26
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:380:13
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:52:16
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:269:32
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:44:16
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:377:17
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:1150:21
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:167:37
at fx (/usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/lib/plugins-middleware.js:579:25)
at onend_request (/usr/local/lib/node_modules/edgemicro/node_modules/microgateway-plugins/accumulate-request/index.js:36:7)
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/lib/plugins-middleware.js:596:31
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:1149:20
at /usr/local/lib/node_modules/edgemicro/node_modules/microgateway-core/node_modules/async/lib/async.js:375:13

The same thing happens with any plugins that send anything as body at the end of onend_request chain, like, for example, json2xml.

This seems like a bug, to me. Is there anybody able to use one of this plugin out of the box?

Any help is very appreciated.

Cheers

Lorenzo