'APP must not be null' on first push if plugin is installed before first app is created

[mbreit]

Steps to reproduce:

1. vagrant destroy && vagrant up
2. vagrant ssh
3. dokku apps:create testapp
4. Create git repository and push to dokku@localhost:testapp

Full output with trace on: https://gist.github.com/mbreit/6b205344a526f02b7136ff8d335dd14d

Revelant lines:

-----> Setting config vars
       CURL_CONNECT_TIMEOUT:  90
remote: + source /var/lib/dokku/core-plugins/available/common/functions
remote: ++ set -eo pipefail
remote: ++ [[ -n 1 ]]
remote: ++ set -x
remote: + [[ ! -n '' ]]
remote: + source /var/lib/dokku/plugins/available/monit/functions
remote: ++ set -eo pipefail
remote: ++ [[ -n 1 ]]
remote: ++ set -x
remote: ++ source /var/lib/dokku/core-plugins/available/common/functions
remote: +++ set -eo pipefail
remote: +++ [[ -n 1 ]]
remote: +++ set -x
remote: ++ source /var/lib/dokku/plugins/available/config/functions
remote: +++ set -eo pipefail
remote: +++ [[ -n 1 ]]
remote: +++ set -x
remote: +++ source /var/lib/dokku/core-plugins/available/common/functions
remote: ++++ set -eo pipefail
remote: ++++ [[ -n 1 ]]
remote: ++++ set -x
remote: ++ source /var/lib/dokku/plugins/available/domains/functions
remote: +++ set -eo pipefail
remote: +++ [[ -n 1 ]]
remote: +++ set -x
remote: +++ source /var/lib/dokku/core-plugins/available/common/functions
remote: ++++ set -eo pipefail
remote: ++++ [[ -n 1 ]]
remote: ++++ set -x
remote: ++ source /var/lib/dokku/plugins/available/certs/functions
remote: +++ set -eo pipefail
remote: +++ [[ -n 1 ]]
remote: +++ set -x
remote: +++ source /var/lib/dokku/core-plugins/available/common/functions
remote: ++++ set -eo pipefail
remote: ++++ [[ -n 1 ]]
remote: ++++ set -x
remote: ++++ dirname /var/lib/dokku/plugins/available/monit/functions
remote: +++ cd /var/lib/dokku/plugins/available/monit
remote: +++ pwd
remote: ++ source /var/lib/dokku/plugins/available/monit/common-functions
remote: +++ set -eo pipefail
remote: +++ [[ -n 1 ]]
remote: +++ set -x
remote: + monit_build_app_config '' set CURL_CONNECT_TIMEOUT
remote: + local app=
remote: ++ dirname /var/lib/dokku/plugins/available/monit/functions
remote: + local plugin_path=/var/lib/dokku/plugins/available/monit
remote: + local dokku_bin=/usr/bin/dokku
remote: + local template_file=/var/lib/dokku/plugins/available/monit/templates/monit.sigil
remote: + local monit_config_file=/home/dokku//monitrc
remote: + domains=($(get_app_domains "$app"))
remote: ++ get_app_domains ''
remote: ++ declare 'desc=return app domains'
remote: ++ verify_app_name ''
remote: ++ declare 'desc=verify app name format and app existence'
remote: ++ local APP=
remote: ++ is_valid_app_name ''
remote: ++ declare 'desc=verify app name format'
remote: ++ local APP=
remote: ++ [[ ! -n '' ]]
remote: ++ dokku_log_fail 'APP must not be null'
remote: ++ declare 'desc=log fail formatter'
remote: ++ echo 'APP must not be null'
remote: APP must not be null
remote: ++ exit 1