code: public AlertConditionCache alertConditions(long policyId)
      {
          AlertConditionCache cache = conditions.get(policyId);
          if(cache == null)
              conditions.put(policyId, cache = new AlertConditionCache(policyId));
          return cache;
      }
docs: Returns the cache of alert conditions for the given policy, creating one if it doesn't exist .
  @param policyId The id of the policy for the cache of alert conditions
  @return The cache of alert conditions for the given policy