private String getDelegateKey(String key) {
		Assert.notNull(key, "cannot be null");
		return namespace + ":" + key;
	}
Wraps a delegate {@link MetadataStore} and adds a prefix to all the handled keys.

Useful for sharing the same {@link MetadataStore} or underlying location without interference
between clients.

@author Marius Bogoevici
extensions/spring-xd-extension-kafka/src/main/java/org/springframework/integration/x/kafka/NamespaceDelegatingMetadataStore.java