Handle PDF Uploads Containing Only Images by Providing a Warning or Notification

[IANTHEREAL]

When uploading a PDF file for vector index construction, the process fails with a 400 Bad Request error from the model because the input text is an empty string.

Upon investigation, it was found that the PDF file contains only an image, and as a result, no characters were extracted from the document. This situation leads to an unsuccessful vector index construction, and the error is not informative enough to guide users.