$ pulumi up
Previewing update (prod):

     Type                 Name           Plan        Info
     pulumi:pulumi:Stack  seniorvu-prod  running     read aws:ec2:Vpc default-vpc-ca0a4ba2
panic: fatal: An assertion has failed

goroutine 1986 [running]:
<http://github.com/pulumi/pulumi/pkg/util/contract.failfast(...)|github.com/pulumi/pulumi/pkg/util/contract.failfast(...)>
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/util/contract/failfast.go:23
<http://github.com/pulumi/pulumi/pkg/util/contract.Assert(...)|github.com/pulumi/pulumi/pkg/util/contract.Assert(...)>
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/util/contract/assert.go:26
<http://github.com/pulumi/pulumi/pkg/resource/plugin.(*provider).Read|github.com/pulumi/pulumi/pkg/resource/plugin.(*provider).Read>(0xc0013bf860, 0xc001a05a80, 0x77, 0x0, 0x0, 0x0, 0xc002b11b00, 0x1817641, 0x4, 0x0, ...)
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/resource/plugin/provider_plugin.go:667 +0xfd6
<http://github.com/pulumi/pulumi/pkg/resource/deploy.(*ReadStep).Apply(0xc002b11b60|github.com/pulumi/pulumi/pkg/resource/deploy.(*ReadStep).Apply(0xc002b11b60>, 0x1, 0x22dd201, 0x23, 0xc001aeee50, 0x3)
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/resource/deploy/step.go:589 +0xfd
<http://github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).executeStep(0xc001888000|github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).executeStep(0xc001888000>, 0xd6, 0x25d28e0, 0xc002b11b60, 0x0, 0x0)
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/resource/deploy/step_executor.go:271 +0x211
<http://github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).executeChain(0xc001888000|github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).executeChain(0xc001888000>, 0xd6, 0xc00225fcc0, 0x1, 0x1)
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/resource/deploy/step_executor.go:221 +0xe6
<http://github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).worker.func1(0xc001888000|github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).worker.func1(0xc001888000>, 0xd6, 0xc00225fcc0, 0x1, 0x1, 0xc001409740)
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/resource/deploy/step_executor.go:371 +0xc8
created by <http://github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).worker|github.com/pulumi/pulumi/pkg/resource/deploy.(*stepExecutor).worker>
	/Users/travis/gopath/src/github.com/pulumi/pulumi/pkg/resource/deploy/step_executor.go:368 +0x2ce