Improve message for working under root directory.

Author: frostming

pipenv/project.py

@@ -29,6 +29,7 @@
     PIPENV_PIPFILE, PIPENV_PYTHON, PIPENV_TEST_INDEX, PIPENV_VENV_IN_PROJECT,
     is_in_virtualenv
 )
+from .exceptions import PipenvUsageError
 from .utils import (
     cleanup_toml, convert_toml_outline_tables, find_requirements,
     get_canonical_names, get_url_name, get_workon_home, is_editable,
@@ -218,6 +219,10 @@ def _build_package_list(self, package_section):
     def name(self):
         if self._name is None:
             self._name = self.pipfile_location.split(os.sep)[-2]
+        if not self._name:
+            raise PipenvUsageError(
+                "Pipenv is not intended to work under root directory, please choose another path."
+            )
         return self._name
 
     @property