Thread:Extension talk:Scribunto/'Equal' character used in template parameter messes things: bug or feature?/reply (2)

That's the way parser function variables work: if you say  and there was no value supplied for parameter , then it outputs the literal string "  ". What you probably want to do is supply a default:  would result in "bar" when nothing is passed for , and   would result in the empty string.

Note also that specifying the empty string (either directly or by passing  where the default is used) is distinct from not specifying the argument at all. In Lua, the empty string comes in as a string while an unspecified parameter comes in as the special value.