Behavior of `realpath` with an empty string argument

[avivkeller]

Refs: #35403

Currently, the project has 2 outcomes for different realpath functions with empty string arguments:

fs.realpathSync('') // Returns CWD
await util.promisify(fs.realpath)('') // Returns CWD

await fs.promises.realpath('') // ENOENT Error
fs.realpathSync.native('') // ENOENT Error
await util.promisify(fs.realpath.native)('') // ENOENT Error

IMO, this should be standardized to
(A) Always throw
(B) Always return CWD
(C) Return CWD for non-.native calls, throw otherwise

[richardlau]

There is always going to be a discrepency between fs.realpath() and fs.promises.realpath().

For some history fs.realpath() and fs.realpathSync() differ from native realpath and have behaviour oddities that were too breaking to change. At one point it was changed to call the native realpath but there were a number of issues that resulted in the implementation being reverted, see #7726.

When fs.promises.realpath() was added the decision was made to call the native realpath since it was a new API and be consistent with fs.realpath.native().

[avivkeller]

I'm aware that there historically have been discrepency, but I think that the discrepencies (for errors) should be handled, or noted in the docs.