Empty string check evaluates wrong

I have a condition checking for empty strings and it is not evaluating an empty string as expected.

I read string one char at a time:

isNumber(s: string) {
  console.log('char', s);
  if (s !== '' && !isNaN(Number(s))) {
    console.log('is a number');
    console.log('-------------');
    return true;
  }
  console.log('NOT a number');
  console.log('-------------');
}

The string is read from a csv file:

a,b,
c,d,e

The 3rd column 1st row is empty but if evaluates to true even though I have s !== '', I have confirmed the char is empty with console. Why is the empty string condition not working?

Update: Could this cause a non empty string? I initialise the variable with quotes then append to it.

cellExtraction = '';
cellExtraction += s; // <- where s should be an empty string read from file