Wiktionary
empty promise
n. (context idiomatic English) A promise that is either not going to be carried out, worthless or meaningless.
Usage examples of "empty promise".
Our conversations were limited to brief greetings, and his empty promise to come home early so that we might have a real visit.
He had almost killed her being bornbig for a baby, an empty promise, for he had failed to grow to the expected size.
He had almost killed her being born-big for a baby, an empty promise, for he had failed to grow to the expected size.
Manie asked wistfully, and Hendrick hesitated on the brink of empty promise.
Together they had agreed Ishido should promise it to him, both knowing this to be an empty promise.