Drag and drop with custom document type not working with WebUI

Studio-side:

1. create a custom document type named lala2019 that extends File
2. add the following XML extension:

   <require>org.nuxeo.ecm.platform.filemanager.service.FileManagerService.Plugins</require>
   <extension target="org.nuxeo.ecm.platform.filemanager.service.FileManagerService" point="plugins">
       <plugin name="DefaultFileImporter" merge="true" docType="lala2019" />
   </extension>
   

3. save project

Server-side:

1. synch the project
2. create a workspace
3. drag and drop a file into the newly-created workspace
4. observe it works fine
5. do a hot reload
6. replay the scenario
7. observe an error is displayed
8. observe an error 500 is displayed in the network tab of the google inspector (see 500error.png)
9. observe an NPE is thrown in the server logs:

   2019-02-19 16:49:28,879 ERROR [http-nio-0.0.0.0-8080-exec-20] [nuxeo-error-log] javax.servlet.ServletException: java.lang.NullPointerException
   	at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoRequestControllerFilter.doFilter(NuxeoRequestControllerFilter.java:190)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.ui.web.auth.NuxeoAuthenticationFilter.doFilterInternal(NuxeoAuthenticationFilter.java:626)
   	at org.nuxeo.ecm.platform.ui.web.auth.service.NuxeoAuthFilterChain.doFilter(NuxeoAuthFilterChain.java:51)
   	at org.nuxeo.ecm.platform.ui.web.auth.oauth.NuxeoOAuthFilter.doFilter(NuxeoOAuthFilter.java:122)
   	at org.nuxeo.ecm.platform.ui.web.auth.service.NuxeoAuthFilterChain.doFilter(NuxeoAuthFilterChain.java:49)
   	at org.nuxeo.ecm.platform.oauth2.NuxeoOAuth2Filter.doFilter(NuxeoOAuth2Filter.java:79)
   	at org.nuxeo.ecm.platform.ui.web.auth.service.NuxeoAuthFilterChain.doFilter(NuxeoAuthFilterChain.java:49)
   	at org.nuxeo.ecm.platform.ui.web.auth.NuxeoAuthenticationFilter.doFilter(NuxeoAuthenticationFilter.java:421)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.exceptionhandling.NuxeoExceptionFilter.doFilter(NuxeoExceptionFilter.java:67)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.encoding.NuxeoEncodingFilter.doFilter(NuxeoEncodingFilter.java:75)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728)
   	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:467)
   	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:392)
   	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:311)
   	at org.nuxeo.ecm.restapi.server.APIServlet.service(APIServlet.java:50)
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.elasticsearch.ElasticSearchFilter.doFilter(ElasticSearchFilter.java:60)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoThreadTrackerFilter.doFilter(NuxeoThreadTrackerFilter.java:43)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoStandbyFilter.doFilter(NuxeoStandbyFilter.java:67)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.core.management.jtajca.internal.Log4jWebFilter.doFilter(Log4jWebFilter.java:69)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.ui.web.rest.FancyURLFilter.doFilter(FancyURLFilter.java:120)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoRequestControllerFilter.doFilter(NuxeoRequestControllerFilter.java:148)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.webdav.service.WIRequestFilter.doFilter(WIRequestFilter.java:61)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoCorsCsrfFilter.doFilter(NuxeoCorsCsrfFilter.java:160)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.exceptionhandling.NuxeoExceptionFilter.doFilter(NuxeoExceptionFilter.java:67)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.encoding.NuxeoEncodingFilter.doFilter(NuxeoEncodingFilter.java:75)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
   	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
   	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
   	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
   	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
   	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
   	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
   	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
   	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
   	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
   	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
   	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
   	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
   	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
   	at java.lang.Thread.run(Thread.java:745)
   Caused by: java.lang.NullPointerException
   	at org.nuxeo.ecm.core.io.marshallers.json.document.DocumentModelJsonWriter.writeEntityBody(DocumentModelJsonWriter.java:140)
   	at org.nuxeo.ecm.core.io.marshallers.json.document.DocumentModelJsonWriter.writeEntityBody(DocumentModelJsonWriter.java:107)
   	at org.nuxeo.ecm.core.io.marshallers.json.ExtensibleEntityJsonWriter.write(ExtensibleEntityJsonWriter.java:79)
   	at org.nuxeo.ecm.core.io.marshallers.json.AbstractJsonWriter.write(AbstractJsonWriter.java:76)
   	at org.nuxeo.ecm.core.io.marshallers.json.DefaultListJsonWriter.write(DefaultListJsonWriter.java:124)
   	at org.nuxeo.ecm.core.io.marshallers.json.document.DocumentModelListJsonWriter.write(DocumentModelListJsonWriter.java:59)
   	at org.nuxeo.ecm.core.io.marshallers.json.document.DocumentModelListJsonWriter.write(DocumentModelListJsonWriter.java:41)
   	at org.nuxeo.ecm.core.io.marshallers.json.AbstractJsonWriter.write(AbstractJsonWriter.java:76)
   	at org.nuxeo.ecm.webengine.jaxrs.coreiodelegate.PartialCoreIODelegate.writeTo(PartialCoreIODelegate.java:119)
   	at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:302)
   	at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1510)
   	at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419)
   	at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409)
   	at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409)
   	at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558)
   	at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733)
   	at org.nuxeo.ecm.webengine.app.jersey.WebEngineServlet.containerService(WebEngineServlet.java:72)
   	at org.nuxeo.ecm.webengine.app.jersey.WebEngineServlet.service(WebEngineServlet.java:56)
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.elasticsearch.ElasticSearchFilter.doFilter(ElasticSearchFilter.java:60)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.webengine.jaxrs.session.SessionCleanupFilter.run(SessionCleanupFilter.java:50)
   	at org.nuxeo.ecm.webengine.jaxrs.HttpFilter.doFilter(HttpFilter.java:49)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.webengine.app.WebEngineFilter$UnitOfWork.doFilter(WebEngineFilter.java:102)
   	at org.nuxeo.ecm.webengine.app.WebEngineFilter$UnitOfWork.access$100(WebEngineFilter.java:79)
   	at org.nuxeo.ecm.webengine.app.WebEngineFilter.doFilter(WebEngineFilter.java:76)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.webengine.jaxrs.context.RequestContextFilter.run(RequestContextFilter.java:48)
   	at org.nuxeo.ecm.webengine.jaxrs.HttpFilter.doFilter(HttpFilter.java:49)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.webengine.app.HeaderFixFilter.run(HeaderFixFilter.java:62)
   	at org.nuxeo.ecm.webengine.jaxrs.HttpFilter.doFilter(HttpFilter.java:49)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.core.management.jtajca.internal.Log4jWebFilter.doFilter(Log4jWebFilter.java:69)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
   	at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoRequestControllerFilter.doFilter(NuxeoRequestControllerFilter.java:178)
   	... 75 more
   

Expected behavior: the drag and drop should be working fine
Note: the same scenario works with JSF UI simply refreshes the page without any UI error but the same exception is present in the logs
Note 2: after checking with dev, filemanger does not support hot reload
Workaround: put the contribution file in $NUXEO_HOME/nxserver/config similar to:

<?xml version="1.0"?>
<component name="my.contribution" version="1.0">
    <require>org.nuxeo.ecm.platform.filemanager.service.FileManagerService.Plugins</require>
    <extension target="org.nuxeo.ecm.platform.filemanager.service.FileManagerService" point="plugins">
        <plugin name="DefaultFileImporter" merge="true" docType="lala2019" />
    </extension>
</component>