code: public Response<ConfigurationSetting> addSetting(String key, String value) {
          return addSetting(new ConfigurationSetting().key(key).value(value));
      }
docs: Adds a configuration value in the service if that key does not exist.
  
  <p><strong>Code Samples</strong></p>
  
  <pre>
  ConfigurationSetting result = client.addSetting("prodDBConnection", "db_connection");
  System.out.printf("Key: %s, Value: %s", result.key(), result.value());</pre>
  
  @param key The key of the configuration setting to add.
  @param value The value associated with this configuration setting key.
  @return The {@link ConfigurationSetting} that was created, or {@code null}, if a key collision occurs or the key
  is an invalid value (which will also throw ServiceRequestException described below).
  @throws IllegalArgumentException If {@code key} is {@code null}.
  @throws ServiceRequestException If a ConfigurationSetting with the same key exists. Or, {@code key} is an empty
  string.