Plugin removing array elements?

[mikob]

I don't understand this behavior:

class FnReplacer extends Visitor {
  visitCallExpression(c: CallExpression): Expression {
    return c;
   }
}
console.log(
  transformSync(`const arr = [1,2,3];`,  {  plugin: (m) => new FnReplacer().visitProgram(m), })
);

outputs incorrectly { code: 'var arr = [\n ,\n ,\n];\n' } (notice there are no digits)

If I do

class FnReplacer extends Visitor {
  visitModule(a) {
    return a;
  }
}

Then it works fine.

I'm trying to make a plugin that replaces all function calls with strings - hence the use of visitCallExpression.