Fix arxiv fetcher not working correctly (JabRef#1780)

* Fix JabRef#1776, remove Cookie Handler implementation, created problems with arxiv
UrlDl works without or own Cookie class, too

* Fix emptyLine

src/main/java/net/sf/jabref/logic/importer/fetcher/ArXiv.java

@@ -71,9 +71,9 @@
 public class ArXiv implements FulltextFetcher, SearchBasedFetcher, IdBasedFetcher {
 
     private static final Log LOGGER = LogFactory.getLog(ArXiv.class);
-
     private static final String API_URL = "http://export.arxiv.org/api/query";
 
+
     @Override
     public Optional<URL> findFullText(BibEntry entry) throws IOException {
         Objects.requireNonNull(entry);
@@ -234,6 +234,7 @@ public Optional<BibEntry> performSearchById(String identifier) throws FetcherExc
         return searchForEntryById(identifier).map(ArXivEntry::toBibEntry);
     }
 
+
     private static class ArXivEntry {
 
         private final Optional<String> title;
@@ -247,6 +248,7 @@ private static class ArXivEntry {
         private final Optional<String> journalReferenceText;
         private final Optional<String> primaryCategory;
 
+
         public ArXivEntry(Node item) {
             // see http://arxiv.org/help/api/user-manual#_details_of_atom_results_returned
 
@@ -302,8 +304,8 @@ public ArXivEntry(Node item) {
 
             // Primary category
             // Ex: <arxiv:primary_category xmlns:arxiv="http://arxiv.org/schemas/atom" term="math-ph" scheme="http://arxiv.org/schemas/atom"/>
-            primaryCategory = XMLUtil.getNode(item, "arxiv:primary_category").flatMap(
-                    node -> XMLUtil.getAttributeContent(node, "term"));
+            primaryCategory = XMLUtil.getNode(item, "arxiv:primary_category")
+                    .flatMap(node -> XMLUtil.getAttributeContent(node, "term"));
         }
 
         /**

src/main/java/net/sf/jabref/logic/net/URLDownload.java

@@ -28,7 +28,6 @@
 import java.io.Reader;
 import java.io.StringWriter;
 import java.io.Writer;
-import java.net.CookieHandler;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;
@@ -79,24 +78,12 @@ public URLDownload(URL source) {
 
         addParameters("User-Agent", "JabRef");
 
-        URLDownload.setCookieHandler();
     }
 
     public URL getSource() {
         return source;
     }
 
-    private static void setCookieHandler() {
-        try {
-            // This should set up JabRef to receive cookies properly
-            if (CookieHandler.getDefault() == null) {
-                CookieHandler.setDefault(new CookieHandlerImpl());
-            }
-        } catch (SecurityException ignored) {
-            // Setting or getting the system default cookie handler is forbidden
-            // In this case cookie handling is not possible.
-        }
-    }
 
     public String determineMimeType() throws IOException {
         // this does not cause a real performance issue as the underlying HTTP/TCP connection is reused