The file for the Sony Walkman NWZ-S638F misses the definition for AudioFolders. I attached a diff for this change to this bug report

udevadm info --query=all --path=/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5
P: /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5
N: bus/usb/001/008
S: libmtp-1-1.5
S: char/189:7
E: UDEV_LOG=3
E: DEVPATH=/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5
E: MAJOR=189
E: MINOR=7
E: DEVNAME=/dev/bus/usb/001/008
E: DEVTYPE=usb_device
E: DRIVER=usb
E: PRODUCT=54c/38e/110
E: TYPE=0/0/0
E: BUSNUM=001
E: DEVNUM=008
E: SUBSYSTEM=usb
E: ID_VENDOR=Sony
E: ID_VENDOR_ENC=Sony
E: ID_VENDOR_ID=054c
E: ID_MODEL=WALKMAN
E: ID_MODEL_ENC=WALKMAN
E: ID_MODEL_ID=038e
E: ID_REVISION=0110
E: ID_SERIAL=Sony_WALKMAN_10FA46F5237186
E: ID_SERIAL_SHORT=10FA46F5237186
E: ID_BUS=usb
E: ID_USB_INTERFACES=:080550:
E: ID_GPHOTO2=1
E: GPHOTO2_DRIVER=proprietary
E: ID_MEDIA_PLAYER=sony_walkman-nwz-s638f
E: ACL_MANAGE=1
E: DEVLINKS=/dev/libmtp-1-1.5 /dev/char/189:7