The attached patch fixes this bug.

if (strlen($value) < 1)

can not work when updating records, we should always use null in these case

this could work:
$value = trim($value);
if ($value === '') {
$value = null;
}

I am not really sure this change would be suitable for 1.9.x - maybe we could add option to allow no number 2.0

Thanks for your comment, Petr - yes, you are right, my first attempt can't work when a non-empty field should be updated to an empty one. The new attached patch (MDL-14788_20080512.patch) works perfectly for me - I tested it under all cases. Your attempt would still display all empty fields as the number 0.

I don't see a need to add an option allowing empty fields - why make things more complicated? Please think how everybody knows a number field to behave in Excel for example - an empty number field will never be implicitly replaced with the number 0 - the way Moodle currently treats the number is simply mathematically wrong. Having a measurement result of 0.002 and having no result at all are completely different cases, however, Moodle would display both values identically, as 0.00 (assuming my patch MDL-14771 has been applied and you have specified 2 decimals). Thus, I really see this as a bug to be fixed in 1.9.1 and not as a new feature.

Hello,
we are very close to 1.9.1, I am afraid minor bugs will have to wait until 1.9.2

thanks for the patch

Now that 1.9.1 is out, can I commit the patch to MOODLE_19_STABLE and HEAD?

+1 for commit for 1.9.2

thanks