FILE_REFERENCE_INVALID

[bobo23]

I try to download profile pictures with upload.getFile. I have the following profile_photo:

profile_photo: {
    _: 'photo',
    flags: 0,
    has_stickers: false,
    id: '1234',
    access_hash: '1234',
    file_reference: Uint8Array(21) [
        0,  96, 166,  99, 56,  32,
      127, 179,  63,  27, 82,  93,
       48, 236, 162, 212, 64, 186,
      219, 111, 203
    ],
    date: 1506954860,
    sizes: [ [Object], [Object], [Object] ],
    dc_id: 4
  },

So I tried to convert the file_reference into a string for my call but always get an FILE_REFERENCE_INVALID error. How can I convert the Uint8Array properly?

Thank you for your help!