[TASK] throw error when market variables in the template are not found in the market while running bd / bdb

[JoernBerkefeld]

right now, if variables were found in the template but not in the market, the variables are stripped from the template and the files are saved without {{{...}}} - as if the variables had an empty string in them.

instead, we should throw an error when a variable was UNDEFINED but allow empty string, null, false and 0 values