docs: private Source getPayloadAsSource(Object replyPayload) {
          if (replyPayload instanceof Source) {
              return (Source) replyPayload;
          } else if (replyPayload instanceof Document) {
              return new DOMSource((Document) replyPayload);
          } else if (replyPayload instanceof String) {
              return new StringSource((String) replyPayload);
          } else {
              throw new CitrusRuntimeException("Unknown type for reply message payload (" + replyPayload.getClass().getName() + ") " +
                      "Supported types are " + "'" + Source.class.getName() + "', " + "'" + Document.class.getName() + "'" + 
                      ", or '" + String.class.getName() + "'");
          }
      }