empty numbers parsed as NaN values create issues in where data should be immutable

[mbarto]

Currently empty numbers are parsed as NaN values by parseDBF.
Since NaN !== NaN, if I compare two such values I always get they are not equal.
Could it be possible to parse those values as undefined or null?

e.g.

switch (type) {
    case 'N':
    case 'F':
    case 'O':
      return parseFloat(textData, 10) || undefined;

[calvinmetcalf]

hm yeah that code doesn't do what its intending to do