presto-hive/src/main/java/io/prestosql/plugin/hive/HiveCoercionRecordCursor.java/Coercer/assureLoaded
class Coercer:        private void assureLoaded(RecordCursor delegate, int field)
        {
            if (!loaded) {
                isNull = delegate.isNull(field);
                if (!isNull) {
                    coerce(delegate, field);
                }
                loaded = true;
            }
        }