deleting parent vocabularies causes build failure

After creating a Child Vocabulary, or a Hierarchical vocabulary, if we delete the parent vocabulary this type of error shows up (see below) and make it impossible to build the jar anymore with Studio.
Studio should at least warn the user about possible effects of deleting parent vocabularies that are used by other vocabularies, or forbid it.
javax.servlet.ServletException: javax.servlet.ServletException: org.nuxeo.studio.client.model.StudioException: Failed to build project: sample-project

at org.nuxeo.studio.servlet.StudioServlet.service(StudioServlet.java:75)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.ecm.webengine.app.WebEngineFilter.doFilter(WebEngineFilter.java:115)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.wss.servlet.BaseWSSFilter.doFilter(BaseWSSFilter.java:106)

at org.nuxeo.wss.servlet.FailSafeWSSFilter.doFilter(FailSafeWSSFilter.java:42)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.connect.filter.SudoFilter.doFilter(SudoFilter.java:50)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.connect.filter.ConnectUrlFilter.doFilter(ConnectUrlFilter.java:107)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.ecm.platform.ui.web.rest.FancyURLFilter.doFilter(FancyURLFilter.java:127)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoRequestControllerFilter.doFilter(NuxeoRequestControllerFilter.java:142)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.ecm.platform.ui.web.auth.NuxeoAuthenticationFilter.doFilter(NuxeoAuthenticationFilter.java:492)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.platform.login.web.LoginStackCleaner.doFilter(LoginStackCleaner.java:49)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.nuxeo.ecm.platform.web.common.exceptionhandling.NuxeoExceptionFilter.doFilter(NuxeoExceptionFilter.java:80)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)

at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)

at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:291)

at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:769)

at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:698)

at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:891)

at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)

at java.lang.Thread.run(Thread.java:662)

Caused by: javax.servlet.ServletException: org.nuxeo.studio.client.model.StudioException: Failed to build project: sample-project

at org.nuxeo.studio.servlet.StudioServlet.doBuildProject(StudioServlet.java:155)

at org.nuxeo.studio.servlet.StudioServlet.doGet(StudioServlet.java:84)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)

at org.nuxeo.studio.servlet.StudioServlet.service(StudioServlet.java:68)

... 44 more

Caused by: org.nuxeo.studio.client.model.StudioException: Failed to build project: sample-project

at org.nuxeo.studio.core.impl.DefaultProject.build(DefaultProject.java:334)

at org.nuxeo.studio.servlet.StudioServlet.doBuildProject(StudioServlet.java:123)

... 47 more

Caused by: java.lang.NullPointerException

at org.nuxeo.studio.core.builders.LayoutFeatureBuilder.getParentVocabulary(LayoutFeatureBuilder.java:272)

at org.nuxeo.studio.core.builders.LayoutFeatureBuilder.build(LayoutFeatureBuilder.java:117)

at org.nuxeo.studio.core.builders.DocumentFeatureBuilder.build(DocumentFeatureBuilder.java:63)

at org.nuxeo.studio.core.builders.DocumentFeatureBuilder.build(DocumentFeatureBuilder.java:28)

at org.nuxeo.studio.core.impl.DefaultProject.doBuild(DefaultProject.java:413)

at org.nuxeo.studio.core.impl.DefaultProject._build(DefaultProject.java:365)

at org.nuxeo.studio.core.impl.DefaultProject.build(DefaultProject.java:332)

... 48 more