Invalid FlatZinc generated

[anonymous192837]

This model generates invalid FlatZinc:

array[1..1] of var bool: arr ::output = let {
  array[1..1] of var bool: res;
  constraint res[1];
} in res;

solve satisfy;

% Error: syntax error, unexpected FZ_BOOL_LIT in line no. 1

Namely:

array [1..1] of var true: arr:: output_array([1..1]) = [true];
array [1..1] of var bool: X_INTRODUCED_0_ ::var_is_introduced  = [true];
solve  satisfy;