Suggest reorganizing this as:

if (point !== null) {
  series.push([x, point]);
} else {
  series.push([x, errorBars ? [null, null] : customBars ? [null, null, null] : point]);
}

or

if (point !== null) {
  series.push([x, point]);
} else {
  if (errorBars) {
    series.push([x, [null, null]]);
  } else if (customBars) {
    series.push([x, [null, null, null]]);
  } else {
    series.push([x, point]);
  }
}

to bring the common case (non-null) to the top and involve dropping through fewer conditionals.