phpGrid automatically sets the validation rules to check for data types that match with the DB field type. This works for the most part except when the value is NULL since NULL is not a value. One will get

In this case, custom data validation comes to the rescue 

Basically, you want to return 'true' when the value is integer AND null, which will subsequently become SQL NULL when saved. 

Pseudo code

[javascript]

function price_validation1(value, colname) {
    if(value === null || Number.isInteger(value)){
      return [true, ""]
    }
   return [false,colname + " must be null a positive integer."];
}

[php]
$dg->set_col_customrule('buyPrice', 'price_validation1');