private static <K, V> void copyMapEntry(Map<K, V> destMap,
                                            Map<K, ? extends V> srcMap,
                                            K key) {
        if (srcMap.containsKey(key)) {
            destMap.put(key, srcMap.get(key));
        }
    }
Copy entry from one map into another.

@param destMap   The map to copy entries into.
@param srcMap    The map to copy entries from.
@param key       The entry with this key will be copied
@param <K>       The map key type.
@param <V>       The map value type.
clients/src/main/java/org/apache/kafka/common/security/ssl/SslFactory.java