This file is indexed.

/usr/share/X11/xkb/symbols/empty is in xkb-data 2.16-1ubuntu1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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default  partial alphanumeric_keys modifier_keys
xkb_symbols "basic" {
    name[Group1]= "Empty";
};