dominikh@dominikh-pc $ go run demo.go
convertUntyped(x = nil (constant nil), target = struct{})
INTERNAL PANIC: unreachable
panic: unreachable [recovered]
        panic: unreachable

goroutine 1 [running]:
code.google.com/p/go.tools/go/types.func·003()
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/check.go:120 +0x16a
code.google.com/p/go.tools/go/types.unreachable()
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/errors.go:24 +0x53
code.google.com/p/go.tools/go/types.(*checker).convertUntyped(0xc21004c120, 0xc21004f9c0, 0x7f7dd4976fe0, 0xc2100245a0)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/expr.go:627 +0x5ba
code.google.com/p/go.tools/go/types.(*checker).assignment(0xc21004c120, 0xc21004f9c0, 0x7f7dd4976fe0, 0xc2100245a0, 0xc21004f901, ...)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/stmt.go:34 +0x199
code.google.com/p/go.tools/go/types.(*checker).assign(0xc21004c120, 0x7f7dd4976f90, 0xc21004f940, 0xc21004f9c0)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/assignments.go:58 +0x2df
code.google.com/p/go.tools/go/types.(*checker).declareVar(0xc21004c120, 0xc21004f940, 0x7f7dd4976d58, 0xc210042480, 0x7f7dd4976d90, ...)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/resolver.go:458 +0x7f8
code.google.com/p/go.tools/go/types.(*checker).declStmt(0xc21004c120, 0x7f7dd4976e00, 0xc21004f700)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/resolver.go:620 +0xcac
code.google.com/p/go.tools/go/types.(*checker).stmt(0xc21004c120, 0x7f7dd4976e38, 0xc21000a620)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/stmt.go:315 +0x3c9b
code.google.com/p/go.tools/go/types.(*checker).stmtList(0xc21004c120, 0xc21000a660, 0x1, 0x1)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/stmt.go:266 +0x68
code.google.com/p/go.tools/go/types.check(0xc21004f740, 0x5c5100, 0x6, 0xc21004f580, 0x7f7dd48dbe90, ...)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/check.go:172 +0x572
code.google.com/p/go.tools/go/types.(*Context).Check(0xc21004f740, 0x5c5100, 0x6, 0xc21004f580, 0x7f7dd48dbe90, ...)
        /home/dominikh/prj/go/src/code.google.com/p/go.tools/go/types/api.go:143 +0x6c
main.main()
        /tmp/demo.go:20 +0x1f8

goroutine 2 [runnable]:
exit status 2