Mkfs.f2fs on null_blk device

[Sijie Lan]

When I try to make f2fs on null_blk device, it always shows "Device
size is not sufficient for F2FS volume",
I am I gave enough space for the file system, i.e, 20GiB. I just want
to know hot to fix it.
this is the output message:
[sijie@fedora null_blk]$ sudo mkfs.f2fs -f -m  /dev/nullb1

    F2FS-tools: mkfs.f2fs Ver: 1.15.0 (2022-05-13)

Info: Disable heap-based policy
Info: Debug level = 0
Info: Trim is enabled
Info: Host-managed zoned block device:
      20 zones, 2147483648 zone size(bytes), 10 randomly writeable zones
      524288 blocks per zone
Info: Segments per section = 1024
Info: Sections per zone = 1
Info: sector size = 4096
Info: total sectors = 10485760 (40960 MB)
Info: zone aligned segment0 blkaddr: 524288
Error: Device size is not sufficient for F2FS volume
Error: Failed to prepare a super block!!!
Error: Could not format the device!!!