Smartthings parent method call error

gistfile1.groovy

// In Device Type App

def poll() {
    log.debug "Executing 'poll'"
    results = parent.pollChildren()
    log.debug results
}

// In Service Manager App

def pollChildren() {
    log.debug "pollChildren"
    return "This works!"
}

// Results
/*
"Executing 'poll'" is logged
and 
error groovy.lang.MissingPropertyException: No such property: results for class: script14187380157011302195780
/*