How can i use "metric.state" using stackdiver datasource in filter?

Hi,

I meet error as below

message:"{ "error": { "code": 400, "message": "Field filter had an invalid value of \"metric.type=\"agent.googleapis.com/memory/percent_used\" metric.state=\"used\"\": The comparison operand: 'state' cannot be used with the prefix 'metric'.", "status": "INVALID_ARGUMENT" } } "

How to use “metric.state” in the filter?