• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: macOS 10.13.6
• Poetry version: 0.12.3
• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/bi1yeu/41b2180afd838560daa0faf68e9c236b

Issue

Hi! This is my first time attempting to use poetry. I created a new empty project with this command:

$ poetry new example

Then, from within the example directory, I attempt to add the jupyter package:

$ poetry add jupyter
Using version ^1.0 for jupyter

Updating dependencies
Resolving dependencies... (4.0s)

[AttributeError]
EmptyConstraint instance has no attribute 'min'

add [-D|--dev] [--git GIT] [--path PATH] [-E|--extras EXTRAS] [--optional] [--python PYTHON] [--platform PLATFORM] [--allow-prereleases] [--dry-run] [--] <name> (<name>)...

Verbose output is contained within the gist linked above. I am able to add other packages without apparent error. Happy to provide additional info.