Wt

In the JS code of the WTextEdit, upon a clipboard paste event, code is executed to ensure that images can be pasted correctly.
The images are inserted as a data URL.

To check whether the pasted content is actually an image, a check is executed for each i, that looks like:

let t = event.clipboardData.types[i];
if ((t.indexOf("image/") === 0) || (t.type.indexOf("image/") === 0)) {
  // create image from data URL
}

Here, the t.type is suspect. The t itself ought to contain a string with a MIME type, according to MDN documentation.
It seems that an older refactoring broke this. The check used to be on clipboardData.types[i] and clipboardData.items[i].type.