code: @Override
      public AddRoleToDBClusterResult addRoleToDBCluster(AddRoleToDBClusterRequest request) {
          request = beforeClientExecution(request);
          return executeAddRoleToDBCluster(request);
      }
docs: <p>
  Associates an Identity and Access Management (IAM) role from an Neptune DB cluster.
  </p>
  
  @param addRoleToDBClusterRequest
  @return Result of the AddRoleToDBCluster operation returned by the service.
  @throws DBClusterNotFoundException
  <i>DBClusterIdentifier</i> does not refer to an existing DB cluster.
  @throws DBClusterRoleAlreadyExistsException
  The specified IAM role Amazon Resource Name (ARN) is already associated with the specified DB cluster.
  @throws InvalidDBClusterStateException
  The DB cluster is not in a valid state.
  @throws DBClusterRoleQuotaExceededException
  You have exceeded the maximum number of IAM roles that can be associated with the specified DB cluster.
  @sample AmazonNeptune.AddRoleToDBCluster
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/neptune-2014-10-31/AddRoleToDBCluster" target="_top">AWS API
  Documentation</a>