nextpnr bug?

meawoppl@monolith:~/repos/MagicSchoolBus$ nextpnr-ice40 --up5k --package sg48 --json magicschoolbus.json --pcf pins.pcf --asc output.asc
Info: Importing module top
Info: Rule checker, verifying imported design
Info: Checksum: 0xdfdd0537

Info: constrained 'ledR' to bel 'X6/Y31/io0'
Info: constrained 'ledB' to bel 'X5/Y31/io0'
Info: constrained 'ledG' to bel 'X4/Y31/io0'
Info: constrained 'pwmOut[0]' to bel 'X17/Y31/io0'
Info: constrained 'pwmOut[1]' to bel 'X8/Y31/io1'
Info: constrained 'pwmOut[2]' to bel 'X8/Y31/io0'
Info: constrained 'pwmOut[3]' to bel 'X9/Y31/io1'
Info: constrained 'pwmOut[4]' to bel 'X9/Y31/io0'
Info: constrained 'pwmOut[5]' to bel 'X13/Y31/io1'
Info: constrained 'pwmOut[6]' to bel 'X13/Y31/io0'
Info: constrained 'pwmOut[7]' to bel 'X16/Y31/io1'
Info: constrained 'tx' to bel 'X19/Y31/io0'
Info: constrained 'miso' to bel 'X9/Y0/io1'
Info: constrained 'mosi' to bel 'X7/Y0/io1'
Info: constrained 'sck' to bel 'X6/Y0/io0'
Info: constrained 'cs' to bel 'X5/Y0/io0'
Info: constrained 'sdn' to bel 'X8/Y0/io0'
Info: constrained 'cameraClock' to bel 'X13/Y0/io1'
Info: constrained 'ccClock' to bel 'X17/Y0/io0'
Info: constrained 'ccData' to bel 'X15/Y0/io0'
Info: constrained 'ccSync' to bel 'X19/Y31/io1'

Info: Packing constants..
Info: Packing IOs..
Info: ledR use by SB_RGBA_DRV/SB_RGB_DRV myLedController.led_driver, not creating SB_IO
Info: ledG use by SB_RGBA_DRV/SB_RGB_DRV myLedController.led_driver, not creating SB_IO
Info: ledB use by SB_RGBA_DRV/SB_RGB_DRV myLedController.led_driver, not creating SB_IO
Info: ccData feeds SB_IO dataI2C, removing $nextpnr_iobuf ccData.
Info: Packing LUT-FFs..
Info:      336 LCs used as LUT4 only
Info:      179 LCs used as LUT4 and DFF
Info: Packing non-LUT FFs..
Info:      126 LCs used as DFF only
Info: Packing carries..
Info:       49 LCs used as CARRY only
Info: Packing RAMs..
Info: Placing PLLs..
Info: Packing special functions..
Info:   constrained ICESTORM_HFOSC 'myClockController.main_osc_OSC' to X0/Y31/hfosc_1
terminate called after throwing an instance of 'nextpnr_ice40::assertion_failure'
  what():  Assertion failure: is_string (/home/meawoppl/repos/nextpnr/common/nextpnr.h:340)
Aborted (core dumped)