jQuery - Accept decimal/numeric and null values from array of text fields

Hi, I am looking a jQuery code that able to validate either decimal/numeric values and also null values from array of text fields. Basically, I managed to validate values from array of text fields but unable to validate the value itself whether it is numeric or null or alphabet. my text field name is testdata[] and it supposes to accept numeric/decimal or null values.

There's no way for a user to enter a literal null value into a text field; by null value do you mean an empty string?