Salesforce: Clone QuoteLineItems from Quote

gistfile1.java

try {
    String sourceId = '0Q0i00000019TdOCAU';
    String destinationId = null; //'0Q0i00000019TdTCAU';
    String query = 'select Quoteid, PricebookEntryId, Quantity, UnitPrice, Discount, Description, ServiceDate, ListPrice, Subtotal, TotalPrice ';
    // get all of the custom, writeable fields
    Map<String, Schema.SObjectField> fieldMap = QuoteLineItem.getSObjectTypE().getDescribe().fields.getMap();
    for (String key : fieldMap.keySet()) {
        Schema.SObjectField field = fieldMap.get(key);
        Schema.DescribeFieldResult result = field.getDescribe();
        if (result.isCustom() && !result.isCalculated()) {
            query += ' ,'+result.getName();
        }
    }
    query += ' from QuoteLineItem where QuoteId = :sourceId LIMIT 122';

    List<QuoteLineItem> q1List = Database.query(query);
    for (QuoteLineItem q1 : q1List) {
        QuoteLineItem q2 = q1.clone();
        if (destinationId != null) {
           q2.QuoteId = destinationId;
        }
        insert q2;
    }
} catch(DMLException e) {
    System.debug(e.getMessage());
    return null;
}