Currently if I have a custom bean (MyBean) and I use it with MediaType.MULTIPART_FORM_DATA content type and MultipartForm annotation in a rest service (MyService.createMyBean()) if some property is null an NPE is thrown. I think with a small modification in resteasy.plugins.providers.multipart.AbstractMultipartFormDataWriter these null properties could be simply skipped. As in multipart/form-data every part has a name it's not a problem if some parts are not present.

Suggested modification in resteasy.plugins.providers.multipart.AbstractMultipartFormDataWriter:
protected void writeParts(MultipartOutput multipartOutput, OutputStream entityStream, byte[] boundaryBytes) throws IOException
{
MultipartFormDataOutput form = (MultipartFormDataOutput) multipartOutput;
for (Map.Entry<String, OutputPart> entry : form.getFormData().entrySet())

{ + if (entry.getValue().getEntity() == null) + continue; MultivaluedMap<String, Object> headers = new MultivaluedMapImpl<String, Object>(); headers.putSingle("Content-Disposition", "form-data; name=\"" + entry.getKey() + "\""); writePart(entityStream, boundaryBytes, entry.getValue(), headers); }

}

MyBean.java:
public class MyBean
{
@FormParam("someBinary")
@PartType(MediaType.APPLICATION_OCTET_STREAM)
private InputStream someBinary;

public InputStream getSomeBinary()

{ return someBinary; }

public void setSomeBinary(InputStream someBinary)

{ this.someBinary = someBinary; }

}

MyService.java:
@Path("/mime")
public class MyService
{

@GET
@Produces(MediaType.MULTIPART_FORM_DATA)
@MultipartForm
public MyBean createMyBean()

{ MyBean myBean = new MyBean(); myBean.setSomeBinary(null); return myBean; }

}