Fish shell Add a directory to the path, but only if it exists

Add a directory to the path, but only if it exists.

function add_path_maybe -d "Add a directory to the path, but only if it exists"
# If the path exists...
if test -d $argv[1]
# ...and if it's not already in the PATH...
if not contains $argv[1] $PATH
# ...push it to the start of the path.
set PATH $argv[1] $PATH
end
end
end