Error no p gain specified for pid

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Hi, I'm using ros-melodic with gazebo on ubuntu 14.04. I have seen similar errors and tried all of them but still unable to solve mine. Here is the text that is stored in config file.

robo:
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50  

  joint1_position_controller:
    type: position_controllers/JointPositionController
    joint: joint1
    pid_gain:
      p: 10.0
      i: 0.0
      d: 0.1

  joint2_position_controller:
    type: position_controllers/JointPositionController
    joint: joint2
    pid_gain:
      p: 10.0
      i: 0.0
      d: 0.1

  joint3_position_controller:
    type: position_controllers/JointPositionController
    joint: joint_left_up_cap
    pid_gains: {p: 200, i: 0.01, d: 0.001}
  joint4_position_controller:
    type: position_controllers/JointPositionController
    joint: joint_right_up_cap
    pid_gains: {p: 200, i: 0.01, d: 0.001}

As you can see I have tried several formats but none worked out.