code: public CMAPreviewApiKey fetchOne(String spaceId, String keyId) {
      assertNotNull(spaceId, "entry");
      assertNotNull(keyId, "keyId");
  
      return service.fetchOne(spaceId, keyId).blockingFirst();
    }
docs: Fetch only one preview api key.
  <p>
  This method will override the configuration specified through
  {@link CMAClient.Builder#setSpaceId(String)} and will ignore
  {@link CMAClient.Builder#setEnvironmentId(String)}.
  
  @param spaceId the id of the space this is valid on.
  @param keyId   the id of the key itself.
  @return one preview api key.
  @throws IllegalArgumentException if spaceId is null.
  @throws IllegalArgumentException if keyId is null.