private static <K, V, M extends Map<K,V>>
    BinaryOperator<M> mapMerger(BinaryOperator<V> mergeFunction) {
        return (m1, m2) -> {
            for (Map.Entry<K,V> e : m2.entrySet()) {
                m1.merge(e.getKey(), e.getValue(), mergeFunction);
            }
            return m1;
        };
    }
A number of collectors specialized for entities. These are inspired by the
{@link java.util.stream.Collectors} class in the java standard libraries.

@author Emil Forslund
@since  3.0.2
runtime-parent/runtime-field/src/main/java/com/speedment/runtime/field/collector/FieldCollectors.java