public static <K, V> Map<K, V> of(K k1, V v1) {
        return Collections.singletonMap(k1, v1);
    }
Returns an unmodifiable map containing a single mapping.

@param <K> the Map's key type
@param <V> the Map's value type
@param k1 the mapping's key
@param v1 the mapping's value
@return a Map containing the specified mapping
@throws NullPointerException if the key or the value is {@code null}
smithy-utils/src/main/java/software/amazon/smithy/utils/MapUtils.java