locarepo: also fastpath `nullid` lookup in __getitem__
We already use that fastpath for `"null"` and `nullrev`, using it for `nullid`
is similar.
Differential Revision: https://phab.mercurial-scm.org/D7486
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2