Map get blank value when I call get method

Question

I have a trigger that when I insert data into a custom object create a map with the id of a contact as a key and a list of the custom object as the value, when I check if the key is contained in the map I get true, but when I try to get the value I get (), but when I filled the map I check if the list has items with an if list.size()>0, this is my code:

    for(Id id : Ids){
        Boolean accs = false;
        Boolean cs = false;
        List<npe03__Recurring_Donation__c> rdOld = new List<npe03__Recurring_Donation__c>();
        for(npe03__Recurring_Donation__c rd : rds){
            if(rd.npe03__Organization__c != null && !cs){
                if(id == rd.npe03__Organization__c){
                    rdOld.add(rd);
                    accs = true;
                }
            }
            else if(rd.npe03__Contact__c != null && !accs){
                if(id == rd.npe03__Contact__c){
                    rdOld.add(rd);
                    cs = true;
                }
            }
        }
        if(rdOld.size()>0){
            rdsMap.put(id, rdOld);
            accs = false;
            cs = false;
        }
    }

for(npe03__Recurring_Donation__c rdNew : trigger.new){
     if(rdNew.Tipo_de_Compromiso__c == 'Nuevo por Aumento'){
         if(rdNew.npe03__Contact__c != null){
                    if(rdsMap.containsKey(rdNew.npe03__Contact__c)){
                        List<npe03__Recurring_Donation__c> rdsSort = new List<npe03__Recurring_Donation__c>();
                        List<npe03__Recurring_Donation__c> rdsOld = rdsMap.get(rdNew.npe03__Contact__c).clone();

                        integer targetsize = rdsOld.size();
                        while(rdsSort.size() != targetsize){
                            datetime dt = Datetime.newInstance(1900, 1, 1, 00, 00, 00);
                            integer i = 0;
                            integer mini = 0;
                            for(i = 0; i != rdsOld.size(); i ++){
                                if(rdsOld[i].CreatedDate > dt){
                                    dt = rdsOld[i].CreatedDate;
                                    mini = i;
                                }
                            }
                            rdsSort.add(rdsOld[mini]);
                            rdsOld.remove(mini);           
                        }
                        if(rdsSort.size()>0 && rdsSort[0].npe03__Amount__c < rdNew.npe03__Amount__c){

                        }
                        else{
                            rdNew.addError('No puede crear un Compromiso de Donación con el Tipo de Compormiso "Nuevo por Aumento", porque el monto ingresado es menor o igual que el monto del Compromiso de Donación Anterior');
                        }
                    }
                }
}

Answer 1

You are removing items from the lists that are the values of the map in this line:

rdsOld.remove(mini);

and so potentially can empty the lists. (Apex works "by reference" meaning when you get the value from the map you are not getting a copy of the list items but are just getting a pointer to the single copy of the list items so if you change them you change them for all references.)

Perhaps you need to make a copy of the list to avoid that:

... rdsOld = rdsMap.get(rdNew.npe03__Contact__c).clone();

so for each iteration over trigger.new you are using the populated list.