/etc/collectd/mysql.conf:
  file.managed:
    - source: salt://misc/collectd/files/mysql.conf
    - template: jinja
    - Defaults:
        MasterStats: 'false'


cat files/mysql.conf
LoadPlugin mysql
<Plugin "mysql">
  <Database "localhost">
    Host "localhost"
    User "USER"
    Password "PASSWORD"
    # Since version 5.0:
    Port "3306"
    MasterStats {{ MasterStats }}
  </Database>
</Plugin>


salt-call state.sls collected
SaltRenderError: Jinja variable 'MasterStats' is undefined; line 14
              ---
              [...]
                  Host "localhost"
                  User "USER"
                  Password "PASSWORD"
                  # Since version 5.0:
                  Port "3306"
                  MasterStats {{ MasterStats }}    <======================
                </Database>

              </Plugin>