Setting null value to multi-select field.

Code Used :

nlapiSetFieldValues(‘custbody11’,”);

This code looks correct at first look but in actual Multiselect field need array for setting data

So if you want to add field you have to use

nlapiSetFieldValues(‘custbody11’,[1,2,3,4]);

Same way if you add array without any value will solve the issue.

So use nlapiSetFieldValues(‘custbody11’,[]); to remove the all values.