code: public Injector get() throws GuacamoleException {
  
          // Return existing Injector if already created
          Injector value = injector.get();
          if (value != null)
              return value;
  
          // Explicitly create and store new Injector only if necessary
          injector.compareAndSet(null, create());
  
          // Consistently return the same Injector, even if two create operations
          // happen concurrently
          return injector.get();
  
      }
docs: Returns a common, singleton instance of a Guice Injector, configured for
  the injections required by the JDBC authentication extension. The result
  of the first call to this function will be cached statically within this
  class, and will be returned for all subsequent calls.
  
  @return
  A singleton instance of the Guice Injector used across the entire
  JDBC authentication extension.
  
  @throws GuacamoleException
  If the Injector cannot be created due to an error.