Fix NPE in builder when renaming a feature

2017-06-02 10:02:33,499 ERROR [catalina-exec-5069] [org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/nuxeo]] Exception while dispatching incoming RPC call
com.google.gwt.user.server.rpc.UnexpectedException: Service method 'public abstract java.lang.String com.nuxeo.studio.client.rpc.StudioService.renameFeature(java.lang.String,com.nuxeo.studio.client.model.FeatureM
odel,java.lang.String) throws com.nuxeo.studio.exception.ProjectNotFoundException,com.nuxeo.studio.exception.BranchNotFoundException,java.io.IOException,com.nuxeo.studio.client.model.ValidationErrorBundle,com.nux
eo.studio.exception.MergeException,com.nuxeo.studio.exception.TargetPlatformNotFoundException' threw an unexpected exception: java.lang.NullPointerException
        at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:416)
        at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:605)
        at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:333)
        at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:303)
        at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:373)
        at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)

...

Caused by: java.lang.NullPointerException
        at com.nuxeo.studio.core.builders.OpRestBindingBuilder.refactorAfterRename(OpRestBindingBuilder.java:43)
        at com.nuxeo.studio.core.builders.OpRestBindingBuilder.refactorAfterRename(OpRestBindingBuilder.java:30)
        at com.nuxeo.studio.core.buildservices.FeatureServiceImpl.refactorAfterRename(FeatureServiceImpl.java:176)
        at com.nuxeo.studio.core.buildservices.FeatureServiceImpl.renameFeature(FeatureServiceImpl.java:137)
        at com.nuxeo.studio.servlet.StudioServiceImpl.renameFeature(StudioServiceImpl.java:636)
        at sun.reflect.GeneratedMethodAccessor1880.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:587)
        ... 84 more