Aground game panics on startup

[jdknives]

When runnning aground, the following panic occurs:

$work:aground-game[master] cx  .
error: internal/model/cell.cx:38 trying to assign argument of type 'struct' to symbol 'mat' of type 'Material'
panic: runtime error: index out of range [1] with length 1

goroutine 1 [running, locked to thread]:
github.com/skycoin/cx/cxparser/actions.CheckTypes(0xc000a9ad80)
	/home/work/go/src/github.com/skycoin/cx/cxparser/actions/functions.go:591 +0xddc
github.com/skycoin/cx/cxparser/actions.FunctionDeclaration(0xc00063be00, {0xc0000af860, 0xc000128600, 0x3}, {0xc00085e570, 0x2, 0x2}, {0xc000ac8000, 0x33, 0x40})
	/home/work/go/src/github.com/skycoin/cx/cxparser/actions/functions.go:190 +0x6cf
github.com/skycoin/cx/cxparser/cxparsingcompletor.yyParse({0x8f9778, 0xc00086b9e0})
	/home/work/go/src/github.com/skycoin/cx/cxparser/cxparsingcompletor/parsingcompletor.go:1702 +0x12e7
github.com/skycoin/cx/cxparser/cxparsingcompletor.Parse(...)
	/home/work/go/src/github.com/skycoin/cx/cxparser/cxparsingcompletor/parsingcompletor.go:31
github.com/skycoin/cx/cxparser/cxparsing.Passtwo(0xc00001afc0)
	/home/work/go/src/github.com/skycoin/cx/cxparser/cxparsing/helpers.go:26 +0x34
github.com/skycoin/cx/cxparser/cxparsing.ParseSourceCode({0xc000303900, 0x15, 0x14}, {0xc00014ca00, 0x14, 0x20})
	/home/work/go/src/github.com/skycoin/cx/cxparser/cxparsing/cxparsing.go:108 +0x6e5
main.parseProgram({0x0, {0x8f1218, 0x0}, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, {0x0, ...}, ...}, ...)
	/home/work/go/src/github.com/skycoin/cx/cmd/cx/helpers.go:54 +0x327
main.Run({0xc000128010, 0x1, 0x1})
	/home/work/go/src/github.com/skycoin/cx/cmd/cx/main.go:160 +0x371
main.main()
	/home/work/go/src/github.com/skycoin/cx/cmd/cx/main.go:22 +0x45

CX version used is 0.8.0.

OS is Arch Linux.