code: public static void setContextStrategy(ContextStrategy contextStrategy) {
      if (ContextTrampoline.contextStrategy != null) {
        throw new IllegalStateException("contextStrategy was already set");
      }
  
      if (contextStrategy == null) {
        throw new NullPointerException("contextStrategy");
      }
  
      ContextTrampoline.contextStrategy = contextStrategy;
    }
docs: Sets the concrete strategy for accessing and manipulating the context.
  
  <p>NB: The agent is responsible for setting the context strategy once before any other method
  of this class is called.
  
  @param contextStrategy the concrete strategy for accessing and manipulating the context
  @since 0.9