If typology is undefined return null

src/wiki-normalizer.ts

@@ -164,7 +164,7 @@ class WikiNormalizer extends Transform {
         return typeof instanceOf.mainsnak.datavalue.value.id === 'undefined' ?
           null : instanceOf.mainsnak.datavalue.value.id;
       } catch (err) {}
-    });
+    }).filter((instance) =>  typeof instance !== 'undefined');
   }
 
   /**