code: public function addGlobal($name, $value)
      {
          if ($this->extensionInitialized || $this->runtimeInitialized) {
              if (null === $this->globals) {
                  $this->globals = $this->initGlobals();
              }
  
              if (!array_key_exists($name, $this->globals)) {
                  // The deprecation notice must be turned into the following exception in Twig 2.0
                  @trigger_error(sprintf('Registering global variable "%s" at runtime or when the extensions have already been initialized is deprecated since version 1.21.', $name), E_USER_DEPRECATED);
                  //throw new LogicException(sprintf('Unable to add global "%s" as the runtime or the extensions have already been initialized.', $name));
              }
          }
  
          if ($this->extensionInitialized || $this->runtimeInitialized) {
              // update the value
              $this->globals[$name] = $value;
          } else {
              $this->staging->addGlobal($name, $value);
          }
      }
docs: Registers a Global.
  
  New globals can be added before compiling or rendering a template;
  but after, you can only update existing globals.
  
  @param string $name  The global name
  @param mixed  $value The global value