diff --git a/swh/indexer/metadata_dictionary/npm.py b/swh/indexer/metadata_dictionary/npm.py
--- a/swh/indexer/metadata_dictionary/npm.py
+++ b/swh/indexer/metadata_dictionary/npm.py
@@ -88,9 +88,15 @@
         rdflib.term.URIRef('https://example.org/bugs/')
         """
         if isinstance(d, dict) and isinstance(d.get("url"), str):
-            return URIRef(d["url"])
+            url = d["url"]
         elif isinstance(d, str):
-            return URIRef(d)
+            url = d
+        else:
+            url = ""
+
+        parsed_url = urllib.parse.urlparse(url)
+        if parsed_url.netloc:
+            return URIRef(url)
         else:
             return None
 
diff --git a/swh/indexer/tests/metadata_dictionary/test_npm.py b/swh/indexer/tests/metadata_dictionary/test_npm.py
--- a/swh/indexer/tests/metadata_dictionary/test_npm.py
+++ b/swh/indexer/tests/metadata_dictionary/test_npm.py
@@ -348,7 +348,8 @@
   "author": {
     "name": "foo",
     "url": ""
-  }
+  },
+  "bugs": ""
 }"""
     result = MAPPINGS["NpmMapping"]().translate(package_json)
     assert result == {
@@ -364,6 +365,9 @@
   "author": {
     "name": "foo",
     "url": "http:example.com"
+  },
+  "bugs": {
+    "url": "http:example.com"
   }
 }"""
     result = MAPPINGS["NpmMapping"]().translate(package_json)