Add check for that reader is not null in GetPostData

headless/public/util/generic_url_request_job.cc

Index: headless/public/util/generic_url_request_job.cc
diff --git a/headless/public/util/generic_url_request_job.cc b/headless/public/util/generic_url_request_job.cc
index 3d93ee34d7a7890dfc5ffd90549696af7fef19ca..012f3ed732b58e4bb827fadb21a8113053109cae 100644
--- a/headless/public/util/generic_url_request_job.cc
+++ b/headless/public/util/generic_url_request_job.cc
@@ -272,6 +272,8 @@ std::string GenericURLRequestJob::GetPostData() const {
   DCHECK_EQ(1u, stream->GetElementReaders()->size());
   const net::UploadBytesElementReader* reader =
       (*stream->GetElementReaders())[0]->AsBytesReader();
+  if (!reader)
+    return "";
   return std::string(reader->bytes(), reader->length());
 }