rosparam returns string not yaml array

edit

I'm trying to define an array in yaml file and load into parameter server in launch file. The following bit of code

XmlRpc::XmlRpcValue temp;  
nhp.searchParam("/r_arm/position/my_param", temp);  
ROS_ASSERT(temp.getType() == XmlRpc::XmlRpcValue::TypeArray);

Fails with the assertion that "temp" is an XmlRpcValue::TypeString not an array, even though

rosparam get /r_arm/position/my_param
[0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

shows the array.

They yaml code looks like:

{r_arm:{position:{
     my_param:[0.0,0.0,0.0,0.0,0.0,0.0]
    ,my_param2:[0.0,0.0,0.0,0.0,0.0,0.0]
    },force:{ 
       ...

Any ideas what I am doing wrong?

(ros Groovy version)