[SalesForce] Test if a variable is instance of List regardless of type

There must be one Apex class with name 'Account'.Please rename that class and try again.

Thanks, Raviteja

This should work:

List lst_PartnersAcc = [SELECT CUST_NUM__c
                                             FROM SYSTEMS__c WHERE Account__c IN (Select  AccountId from AccountShare where ( UserOrGroupId IN : map_group OR  UserOrGroupId =:userId )AND RowCause IN ('Territory', 'TerritoryManual', 'TerritoryRule'))
                                             ];
Set tempList = new Set();
for(Systems__c s : lst_PartnersAcc) {
    tempList.add(s.Cust_Num__c);
}
List orders = [select id,name from orders__c WHERE customer_1__c IN :tempList OR customer_2__c IN :tempList ETC...
                                             ];

Just needed to add the Customer Number to the set individually for each Systems__c.