public static <K, V> Map<K, V> requireKeys(Map<K, V> map, K requiredKeyA, K requiredKeyB, K requiredKeyC) {
        requireKeys(map, requiredKeyA);
        requireKeys(map, requiredKeyB);
        requireKeys(map, requiredKeyC);
        return map;
    }
Checks if the provided map contains all the provided required key(s).

@param <K> key type
@param <V> value type
@param map to check
@param requiredKeyA to check for existence
@param requiredKeyB to check for existence
@param requiredKeyC to check for existence
@return the same instance of the provided map
@throws NoSuchElementException if the required keys are not keys in the
provided Map
@throws NullPointerException if the provided Map is null
common-parent/invariant/src/main/java/com/speedment/common/invariant/NullUtil.java