"pdfcpu merge demo.pdf 0_123.pdf" has an error or use golang to code by follow

pdf.MergeCreateFile(${0_123.pdf}, ${demo.pdf}, false,nil)

it will tips:
unexpected panic attack: runtime error: invalid memory address or nil pointer dereference

env:
go version go1.20.4 linux/amd64
pdfcpu version:v0.6.0

PDF file is attached
0_123.pdf:0_123.pdf
demo.pdf:you can use any file or a output path to replace it