Conditionals --> Functions --> Function Expressions

I’m a complete noob - thanks for the help.

I’m on the Conditionals → Functions → Function Expressions (page 8/11) assignment.

I passed the assignment but don’t understand how.
I’d expect the below code to return TRUE, but regardless of the day I enter, it always returns false.
Why is that?

const plantNeedsWater = function (day) {
  if (day === "Wednesday") {
    return true;
  } else {
    return false;
  }
};

plantNeedsWater("Wednesday");
console.log(plantNeedsWater());

Thanks!

Missing argument. Drop the line above, and insert the argument in this line.