gazebo bumper plugin wont give me any data ?

edit

I'm working on nao simulation in gazebo when i call "rostopic echo /nao_robot/fsr" on terminal it gives me a lot of these

---
header: 
  seq: 49
  stamp: 
    secs: 0
    nsecs: 0
  frame_id: RFsrRL_frame
states: []
---

but it actually doesent give me any numbers

while the gztopic gives me a lot of params and numbers

  contact {
  collision1: "nao_v40::r_ankle::r_ankle_collision_RFsrFL_frame"
  collision2: "ground_plane::link::collision"
  position {
    x: -0.42475
    y: 0.9781
    z: -0.00050999999999996664
  }
  position {
    x: -0.42475
    y: 0.9681
    z: -0.00050999999999996664
  }
  position {
    x: -0.43475
    y: 0.9781
    z: -0.00050999999999996664
  }
  position {
    x: -0.43475
    y: 0.9681
    z: -0.00050999999999996664
  }
  normal {
    x: 0
    y: 0
    z: 1
  }
  normal {
    x: 0
    y: 0
    z: 1
  }
  normal {
    x: 0
    y: 0
    z: 1
  }
  normal {
    x: 0
    y: 0
    z: 1
  }
  depth: 0.00050999999999996664
  depth: 0.00050999999999996664
  depth: 0.00050999999999996664
  depth: 0.00050999999999996664
  wrench {
    body_1_name: "nao_v40::r_ankle::r_ankle_collision_RFsrFL_frame"
    body_1_id: 281
    body_2_name: "ground_plane::link::collision"
    body_2_id: 5
    body_1_wrench {
      force {
        x: 0.072087592596782241
        y: 0.028411028459002015
        z: 3.2030964913988988
      }
      torque {
        x: 0.10100978879127898
        y: -0.160708389002122
        z: -0.000847823940497985
      }
    }
    body_2_wrench {
      force {
        x: 0
        y: 0
        z: 3.6714702680842885e+228
      }
      torque {
        x: 2.4711723928230347e-259
        y: 9.3035059818977424e+199
        z: 5.6052338313193757e-67
      }
    }
  }
  wrench {
    body_1_name: "nao_v40::r_ankle::r_ankle_collision_RFsrFL_frame"
    body_1_id: 281
    body_2_name: "ground_plane::link::collision"
    body_2_id: 5
    body_1_wrench {
      force {
        x: 0
        y: 0
        z: 0
      }
      torque {
        x: 0
        y: 0
        z: 0
      }
    }
    body_2_wrench {
      force {
        x: 3.8628231006005092e+174
        y: 9.7782040937894567e+199
        z: 1.5513041645708511e+218
      }
      torque {
        x: 8.0750745817655192e-13
        y: 5.0510556981628804e-85
        z: 5.5510021959412005e+180
      }
    }
  }
  wrench {
    body_1_name: "nao_v40::r_ankle::r_ankle_collision_RFsrFL_frame"
    body_1_id: 281
    body_2_name: "ground_plane::link::collision"
    body_2_id: 5
    body_1_wrench {
      force {
        x: 0
        y: 0
        z: 0
      }
      torque {
        x: 0
        y: 0
        z: 0
      }
    }
    body_2_wrench {
      force {
        x: 1.1892206589683481e+93
        y: 6.1850557490740837e+223
        z: 4.37073153235929e-19
      }
      torque {
        x: 5.8310458343477418e+252
        y: 1.1505135141515544e+248
        z: 3.6718864393444843e+257
      }
    }
  }
  wrench {
    body_1_name: "nao_v40::r_ankle::r_ankle_collision_RFsrFL_frame"
    body_1_id: 281
    body_2_name: "ground_plane::link::collision"
    body_2_id: 5
    body_1_wrench {
      force {
        x: 0
        y: 0
        z: 0
      }
      torque {
        x: 0
        y: 0
        z: 0
      }
    }
    body_2_wrench {
      force {
        x: 1.0854901422561223e+189
        y: 3.6351494492871948e+228
        z: 3.6344582440600231e+228
      }
      torque {
        x: 2.1797885502573651e+243
        y: 4.7019837676989491e+198
        z: 2.9313226905821438e+256
      }
    }
  }
  time {
    sec: 0
    nsec: 1000000
  }
  world: "default"
}

where i'm going wrong ? my definitions are like this :

<gazebo reference="RFsrRL_frame">
    <mu1>0.5</mu1>
    <mu2>0.5</mu2>
    <selfCollide>false</
    <turnGravityOff>false</
    <fdir1>1 0 0</fdir1>
    <maxVel>0.1</maxVel>
    <minDepth>0.003</minDepth>
    <sensor name="RFsrRL" type="contact">
      <always_on>1</always_on>
      <update_rate>20</update_rate>
      <visualize>false</visualize>
      <contact>
        <collision>RFsrRL_frame_
      <!--  <topic>RFsrRL</topic>-->
      </contact>
   <plugin name="gazebo_ros_bumper_ controller" filename="libgazebo_ros_bumper.so">
        <robotNamespace>nao_robot</robotNamespace>
      <alwaysOn>true</alwaysOn>
    <updateRate>20</updateRate>
    <bumperTopicName>fsr</bumperTopicName>
    <frameName>RFsrRL_frame</frameName>
            </plugin>
    </sensor>
  </gazebo>

do i need to add more parameters to plugin section ? or its not even suppose to show anything other than they are already showing ?