Querying leads with null field values
Is there a way to do a query through the rest api to return a set of leads that have no value in a specified field? In results, the returned value will be null, like "firstName" : null. However, when I send a query like "filterType=fieldName&filterValues=null", it does not return the leads whose value in the specified field is empty, it returns the leads whose value in the specified field is literally the word "null".
"filterType=fieldName&filterValues=" also does returns an error, because filter values wants a value.