filename() is unknow

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I downloaded and install nxlog-ce-3.0.2272_rhel8.x86_64.rpm on Centos 8 server
I it is my first installation on centos 8. I used before only Centos 7 with nxlog.
I copied input configuration from other server  . and sending data to graylog
But field FileName now unknown instead name of file . Rest of fields work excellent 

<Input log>
    Module	im_file
    File	"/var/log/*"
    SavePos	TRUE
    ReadFromLast TRUE
	Exec	$Message = $raw_event;
	Exec	$FileName = file_name();