[SalesForce] shortcut way to remove null records from List

The idiomatic way to do this in other languages without iterator semantics is to iterate through the list backwards.

For example:

public static List<Object> removeAll(List<Object> target, Object toRemove) {
    for(Integer i = target.size() - 1; i >= 0; i--) {
        if(target[i].equals(toRemove)) {
            target.remove(i);
        }
    }

    return target;
}

You are getting duplicate values because in both the queries you are using different projections;

List mainGroupLinkerIPGlist = [SELECT Id,Intralinks_Portal_Group__c FROM Intralinks_Group_and_Contact_Links__c where Contact__c = :mainGroupLinker.Contact__c];

And

List toCopy = [SELECT Intralinks_Portal_Group__c FROM Intralinks_Group_and_Contact_Links__c where Contact__c = :copyFrom.Contact__c];

As hashCode of an object depends on values, so for the same object in two list you will get two different hashcode.

So if you can fetch same columns in both the queries then your set will give you the unique items as result.

Example:

List<Account> acc1 = [select Id,name from Account order by createdDate limit 5];
List<Account> acc2 = [select Id from Account order by createdDate limit 6];
List<Account> acc3 = [select Id,name from Account order by createdDate limit 6];


Set<Account> accSet1 = new Set<Account>();
accSet1.addAll(acc1);
accSet1.addAll(acc2);
system.assertEquals(11,accSet1.size());

Set<Account> accSet2 = new Set<Account>();
accSet2.addAll(acc1);
accSet2.addAll(acc3);
system.assertEquals(6,accSet2.size());