
Specify an input file for an extension
insertFile.RdEmits a <type> <file> line. NULL (and length-zero) input is treated
as "parameter omitted" and produces no output, matching how
insertValue() handles NA.

insertFile.RdEmits a <type> <file> line. NULL (and length-zero) input is treated
as "parameter omitted" and produces no output, matching how
insertValue() handles NA.