Steps to reproduce:

1. Create a calculated item
2. In the formula field, I'm referencing a JMX item.**last("hostname:jmx[\"org.apache.activemq:type=Broker,brokerName=localhost,destinationType=Topic,destinationName=XYZ\",\"EnqueueCount\"]")

Result:
In the info column, I get the error message:

Cannot evaluate expression: "Cannot evaluate function "last()": item "hostname:jmx["org.apache.activemq:type=Broker,brokerName=localhost,destinationType=Topic,destinationName=XYZ","EnqueueCount"]" not supported.".

Expected:
I expect the calculated item to be enable and retrieving values from the jmx host.