list directory without BUILD file is doing list ::

[wisechengyi]

$ mkdir abc
$ ./pants list abc/::
WARN] The behavior of `./pants list` (no explicit targets) will soon become a no-op. To remove this warning, please specify one or more explicit target specs (e.g. `./pants list ::`).
src/python/pants/util:meta
src/python/pants/base:build_root
3rdparty/python:ansicolors
3rdparty/python:six
src/python/pants/util:strutil
src/python/pants/util:dirutil
src/python/pants/util:tarutil
...

[stuhood]

Fixed.

Exception caught: (<class 'pants.build_graph.address_lookup_error.AddressLookupError'>)

Exception message: Build graph construction failed: ExecutionError Multiple exceptions encountered:
  ResolveError: Path "blah" contains no BUILD files.```