The most common and most likely answer to this crossword clue is the 6 letter word HOLLOW
I've seen this crossword clue in The Guardian
H
O
L
L
O
W
More clues leading to the result HOLLOW
Buddy explains!

The straight part
We know that "empty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case empty = hollow.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HOLLOW mean?
HOLLOW noun- A small valley between mountains.
- A sunken area or unfilled space in something solid; a cavity, natural or artificial.
- A sunken area.
- A feeling of emptiness.
- To make a hole in something; to excavate
- (of something solid) Having an empty space or cavity inside.
- (of a sound) Distant, eerie; echoing, reverberating, as if in a hollow space; dull, muffled; often low-pitched.
- Without substance; having no real or significant worth; meaningless.
- Insincere, devoid of validity; specious.
- Concave; gaunt; sunken.
- Pertaining to hollow body position
- Completely, as part of the phrase beat hollow or beat all hollow.
- Hey, hello
- To call or urge by shouting; to hollo.