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