Re: [PATCH] odb: do not use "blank" substitute for NULL

> When various *object_info() functions are given an extended object
> info structure as NULL by a caller that does not want any details,
> the code uses a file-scope static blank_oi to pass it down to the
> helper functions they use, to avoid handling NULL specifically.
> 
> The ps/object-read-stream topic graduated to 'master' recently
> however had a bug that assumed that two identically named file-scope
> static variables in two functions are the same, which of course is
> not the case.  This made "git commit" take 0.38 seconds to 1508
> seconds in some case, as reported by Aaron Plattner here:
> 
>   https://lore.kernel.org/git/f4ba7e89-4717-4b36-921f-56537131fd69@nvidia.com/
> 
> We _could_ move the blank_oi variable to a global scope in BSS to
> fix this regression, but explicitly handling the NULL is a much
> safer fix.  It would also reduce the chance of errors that somebody
> accidentally writes into blank_oi, making its contents dirty, which
> potentially will make subsequent calls into the callpath misbehave.
> 
> By explicitly handling NULL input, we no longer have to worry about
> it.