"Attempt to de-reference a null object" for formula field in map

Question

I am trying to get the value of formula field to check in condition via customAccMap. i am checking if formula_field__c is null then i need to throw a cpqException. But on Add Product Page on CPQ i am getting "column 1: Attempt to de-reference a null object". Can anyone please help me.

public static void cannotChooseAcc(List<SBQQ__QuoteLine__c> newLines){

    if(!newLines.isEmpty())
    {   
        Set<Id> customObjectAcc = new Set<Id>();
        for(SBQQ__QuoteLine__c newQL :newLines)
        {   
        if((newQL.OppRecordTypeId__c == Label.newOppRecordTypeId__c)
               customObjectAcc.add(newQL.custom_Account__c);
        }
        Map<Id,custom_Account__c> customAccMap = new Map<Id,custom_Account__c>([Select Id,formula_field__c from custom_Account__c where Id IN : customObjectAcc]);
        if(!customAccMap.isEmpty()){
            for(SBQQ__QuoteLine__c newQL :newLines){

                if(customAccMap.get(newQL.custom_Account__c).formula_field__c == null) {

                     throw new CPQException('You cannot select this account');
                }
            }
        }
    }        
}

Answer 1

A cleaner solution would be to modify the query, and then you just check for the presence of the ID value:

public static void cannotChooseAcc(List<SBQQ__QuoteLine__c> newLines) {
    // Get custom account ID values
    Set<Id> customObjectAcc = new Set<Id>();
    for(SBQQ__QuoteLine__c newQL :newLines) {
        if(newQL.OppRecordTypeId__c == Label.newOppRecordTypeId__c) {
            customObjectAcc.add(newQL.custom_Account__c);
        }
    }
    // Query for accounts with null formula field in the list
    Set<Id> unavailable = new Map<Id, Custom_Account__c>([
        SELECT Id FROM Custom_Account__c WHERE Formula_Field__c = NULL AND Id = :customObjectAcc
    ]).keySet();
    // If the ID is in the Set, the formula was null
    for(SBQQ__QuoteLine__c newQL :newLines){
        if(unavailable.contains(newQL.Custom_Account__c)) {
            throw new CPQException('You cannot select this account');
        }
    }        
}