title: When trying to assign an array to a constant I get undefinded even though the model contains the array and contains strings
body: <p>I have an understanding problem. The following code should read out all strings from a string array with the name 'Was Requested By Who' in the 'Article' model and find the appropriate user. The article is filled, see code below. However after I do the assignment to list I get back an undefined and MongoDb throws the error: Cannot read properties of undefined (reading 'map')</p>
  <p>Controller code to read the array:</p>
  <pre><code>export const AngefragteArtikel = async (req, res) =&gt; {
  try {
  const artikel = await Artikel.find({ userId: req.params.id });
  
  //Show me the code below in the console
  console.log(artikel);
  
  if (!artikel) return res.status(400).json(&quot;Artikel wurde nicht gefunden&quot;);
  
  // liste is undefined
  const liste = artikel.wurdeAngefragtVonWem;
  
  const anfragenListe = await Promise.all(
    liste.map(async (id) =&gt; {
      return await User.find({ _id: id });
    })
  );
  
  res
    .status(200)
    .json(anfragenListe.flat().sort((a, b) =&gt; b.createdAt - a.createdAt));
   } catch (error) {
    console.log(error);
   }
  };
  </code></pre>
  <p>Article object:</p>
  <pre><code>[
    {
  _id: new ObjectId(&quot;6300df5883077b578a1ae7a7&quot;),
  userId: '6300b9b09ec9b44132d78a2c',
  userBild: 'https://firebasestorage.googleapis.com/v0/b/sharing-c83d9.appspot.com/o/profilBild%2F6300b9b09ec9b44132d78a2c?alt=media&amp;token=2de6b424-df54-481b-859f-6b6d5be92359',   
  name: 'NEUER ARTIKEL',
  wurdeAngefragtVonWem: [ '6300b84ada5bcb3c8a2eb52e' ],
  bezeichnung: 'NEUER ARTIKEL',
  art: 'verschenken',
  bild: 'https://firebasestorage.googleapis.com/v0/b/sharing-c83d9.appspot.com/o/artikelBilder%2Fheiligenhafen_graswader.jpg?alt=media&amp;token=fec8d184-15b3-4d89-bca9-ff6b25204489', 
  createdAt: 2022-08-20T13:19:20.165Z,
  updatedAt: 2022-08-20T13:21:22.080Z,
  __v: 0
   }
  ]
  </code></pre>