def policy(name)
      json = client.get("/v1/sys/policy/#{encode_path(name)}")
      return Policy.decode(json)
    rescue HTTPError => e
      return nil if e.code == 404
      raise
    end
def policy(name)
      json = client.get("/v1/sys/policy/#{encode_path(name)}")
      return Policy.decode(json)
    rescue HTTPError => e
      return nil if e.code == 404
      raise
    end
Get the policy by the given name. If a policy does not exist by that name,
 +nil+ is returned.

 @example
   Vault.sys.policy("root") #=> #<Vault::Policy rules="">

 @return [Policy, nil]