What is bash declare built-in reporting here?

Our RHEL8 servers don't have nc available, but at some time in the past someone using this shared account defined an nc function:

-shellsession
$ declare -f nc | head -1
nc ()
$

I am trying to determine where this function is defined:

-shellsession
$ (shopt -s extdebug; declare -F nc)
nc 0 environment
$

I was expecting a line number and a filename there, and as you can see I got 0 environment instead. Can somebody tell me what this means, please?