panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x28 pc=0x8c6d]

goroutine 1 [running]:
runtime.panic(0x251000, 0x5551b9)
/Users/ajhager/opt/go/src/pkg/runtime/panic.c:266 +0xb6
main.writeCommandPackage(0x2106b42a0, 0x210c93d10, 0xa, 0x0, 0x0)
/Users/ajhager/go/src/github.com/neelance/gopherjs/tool.go:561 +0x3ad
main.tool(0x0, 0x0)
/Users/ajhager/go/src/github.com/neelance/gopherjs/tool.go:124 +0x501
main.main()
/Users/ajhager/go/src/github.com/neelance/gopherjs/tool.go:77 +0x26

This is the error I get when trying to 'gopherjs build' botmark at the moment. I am trying to figure out a clearer diagnosis, but I can't find something obviously specific to enj.