Inputs with ARIA-Describedby and ARIA-Labelledby
Summary: In order to not be flagged as a violation in aXe, aria-describedby and aria-labelledby must reference by ID elements within the current document. There is no requirement, however, that the referenced elements must contain text or that the attributes have a value (that is, null values/"" is fine).
Note, however, that if you point an aria-labelledby only at an element that contains no text content, you have effectively erased the text label for that field, since aria-labelledby overrides all other labeling.