Panic while migrating

Issues Dgraph
1 
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x80 pc=0x1be656a]

goroutine 1 [running]:
github.com/dgraph-io/dgraph/dgraph/cmd/migrate.populateReferencedByColumns(0x1e38a60)
	/ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/migrate/table_info.go:250 +0x14a
github.com/dgraph-io/dgraph/dgraph/cmd/migrate.run(0xc00263fcb8)
	/ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/migrate/run.go:121 +0x4e7
github.com/dgraph-io/dgraph/dgraph/cmd/migrate.init.0.func1(0xc00020ef00, {0xc00015b4c0, 0x4, 0x4})
	/ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/migrate/run.go:44 +0x25
github.com/spf13/cobra.(*Command).execute(0xc00020ef00, {0xc00015b440, 0x4, 0x4})
	/go/pkg/mod/github.com/spf13/cobra@v0.0.5/command.go:830 +0x5f8
github.com/spf13/cobra.(*Command).ExecuteC(0x32faa80)
	/go/pkg/mod/github.com/spf13/cobra@v0.0.5/command.go:914 +0x2fc
github.com/spf13/cobra.(*Command).Execute(...)
	/go/pkg/mod/github.com/spf13/cobra@v0.0.5/command.go:864
github.com/dgraph-io/dgraph/dgraph/cmd.Execute()
	/ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/cmd/root.go:81 +0x50
main.main()
	/ext-go/1/src/github.com/dgraph-io/dgraph/dgraph/main.go:112 +0x116