[mlir] Migrate away from ValueRange(std::nullopt) (NFC) (#145210)

ArrayRef has a constructor that accepts std::nullopt.  This
constructor dates back to the days when we still had llvm::Optional.

Since the use of std::nullopt outside the context of std::optional is
kind of abuse and not intuitive to new comers, I would like to move
away from the constructor and eventually remove it.

One of the common uses of std::nullopt is in one of the constructors
for ValueRange.  This patch takes care of the migration where we need
ValueRange() to facilitate perfect forwarding.  Note that {} would be
ambiguous for perfecting forwarding to work.

0 files changed, 0 insertions, 0 deletions