code: private ApplicationDefinition checkApplicationKey(ApplicationDefinition appDef) {
          Tenant tenant = Tenant.getTenant(appDef);
          ApplicationDefinition currAppDef = getApplication(tenant, appDef.getAppName());
          if (currAppDef == null) {
              m_logger.info("Defining application: {}", appDef.getAppName());
          } else {
              m_logger.info("Updating application: {}", appDef.getAppName());
              String appKey = currAppDef.getKey();
              Utils.require(Utils.isEmpty(appKey) || appKey.equals(appDef.getKey()),
                            "Application key cannot be changed: %s", appDef.getKey());
          }
          return currAppDef;
      }
docs: Verify key match of an existing application, if any, and return it's definition.