According to the Wikipedia entry on Asimov, the short story is called "About Nothing" (1975), which first appeared on a postcard and then was included in the Winds of Change and other short stories collection.
About Nothing By Isaac Asimov
All of Earth waited for the small black hole to bring it to its end.
It had been discovered by Professor Jerome Hieronymus at the Lunar
telescope in 2125 and it was clearly going to make an approach close
enough for total tidal destruction.
All of Earth made its wills and wept on each other’s shoulder, saying,
“Good-bye, good-bye, good-bye.” Husbands said good-bye to their wives,
brothers said good-bye to their sisters, parents said good-bye to
their children, owners said good-bye to their pets, and lovers
whispered good-bye to each other.
But as the black hole approached, Hieronymus noted there was no
gravitational effect. He studied it more closely and announced, with a
chuckle, that it was not a black hole after all.
“It’s nothing,” he said. “Just an ordinary asteroid someone has
He was killed by an infuriated mob, but not for that. He was killed
only after he publicly announced that he would write a great and
moving play about the whole episode.
He said, “I shall call it Much Adieu About Nothing.”
All humanity applauded his death.