Installation script fails if ~/.yarn exists but does not contain a Yarn installation

[Daniel15]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
The installation script fails if ~/.yarn exists but does not contain a Yarn installation.

If the current behavior is a bug, please provide the steps to reproduce.

rm -rf ~/.yarn
mkdir ~/.yarn
curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 0.17.9

Results in:

Installing Yarn!
./install.sh: line 164: yarn: command not found

What is the expected behavior?
Installation script should work and install Yarn

[petebacondarwin]

It seems to me that this check:

if [ -n `which yarn` ]; then

is not failing as expected since which yarn is returning something that is not-null even if there is no yarn in the current path.