what is ^@ character in vi?
You can answer the question yourself: at least, the "what character is this" part, not the "how did it get here" part. From :help ga:
Print the ascii value of the character under thecursor in decimal, hexadecimal and octal. Forexample, when the cursor is on a 'R': <R> 82, Hex 52, Octal 122For more details and related commands, see the full entry.