handle records without downloads

core/loaders/doab.py

@@ -393,6 +393,20 @@ def add_by_doab(doab_id, record=None):
                 url_to_provider(dl_url) if dl_url else None,
                 **metadata
             )
+        else:
+            if 'format' in metadata:
+                del metadata['format']
+            edition = load_doab_edition(
+                title,
+                doab_id,
+                '',
+                '',
+                license,
+                language,
+                isbns,
+                None,
+                **metadata
+            )
         return edition
     except IdDoesNotExistError:
         return None

core/loaders/doab_utils.py

@@ -103,6 +103,8 @@ FRONTIERSIN = re.compile(r'frontiersin.org/books/[^/]+/(\d+)')
 
 def online_to_download(url):
     urls = []
+    if not url:
+        return urls
     if url.find(u'mdpi.com/books/pdfview/book/') >= 0:
         doc = get_soup(url)
         if doc: