panic error: query results in "assignment to entry in nil map"

[danielmai]

• What version of Dgraph are you using?
  v1.0.12-rc5, master (06df966)

• Have you tried reproducing the issue with latest release?
  Yes. v1.0.11 works OK.

• Steps to reproduce the issue (command/config used to run Dgraph).

  • Run Dgraph cluster (clean).
  • Run query

  $ curl localhost:8080/query -d '
  {
    var(func: has(pred)) {
      n as uid
      cnt as count(_predicate_)
    }
  
    data(func: uid(n)) @filter(gt(val(cnt), 4)) {
      expand(_all_)
    }
  }'

  or this query

  $ curl localhost:8080/query -d '
  {
    var(func: uid(0x1)) {
      cnt as _predicate_
    }
  
    data(func: uid(0x1)) {
      val(cnt)
    }
  }'

• Result:

2019/02/19 09:48:01 http: panic serving 127.0.0.1:40140: assignment to entry in nil map
goroutine 237 [running]:
net/http.(*conn).serve.func1(0xc0006448c0)
	/snap/go/3129/src/net/http/server.go:1746 +0xd0
panic(0x1379000, 0x15d5cf0)
	/snap/go/3129/src/runtime/panic.go:513 +0x1b9
github.com/dgraph-io/dgraph/query.(*SubGraph).fillVars(0xc00add6580, 0xc00049bbc0, 0xc00048a287, 0x3)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/query/query.go:1705 +0x5a1
github.com/dgraph-io/dgraph/query.(*SubGraph).recursiveFillVars(0xc00add6580, 0xc00049bbc0, 0x0, 0x0)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/query/query.go:1644 +0x39
github.com/dgraph-io/dgraph/query.(*SubGraph).recursiveFillVars(0xc00add62c0, 0xc00049bbc0, 0xc00adbc3c0, 0x1)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/query/query.go:1649 +0xa6
github.com/dgraph-io/dgraph/query.(*QueryRequest).ProcessQuery(0xc00ad59b30, 0x15ebb20, 0xc00ad3b980, 0x1, 0x1)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/query/query.go:2616 +0x61d
github.com/dgraph-io/dgraph/query.(*QueryRequest).Process(0xc00ad59b30, 0x15ebb20, 0xc00ad3b980, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/query/query.go:2710 +0x5e
github.com/dgraph-io/dgraph/edgraph.(*Server).doQuery(0xc000481c40, 0x15ebb20, 0xc00ade4240, 0xc00ad657c0, 0xc00ad13d40, 0x0, 0x0)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/edgraph/server.go:579 +0x639
github.com/dgraph-io/dgraph/edgraph.(*Server).Query(0xc000481c40, 0x15ebb20, 0xc00ad3b890, 0xc00ad657c0, 0x2029de0, 0x2029de0, 0x15ebb20)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/edgraph/server.go:508 +0x9b
github.com/dgraph-io/dgraph/dgraph/cmd/alpha.queryHandler(0x15eaa60, 0xc00ad321c0, 0xc000044600)
	/home/dmai/go/src/github.com/dgraph-io/dgraph/dgraph/cmd/alpha/http.go:169 +0x2f4
net/http.HandlerFunc.ServeHTTP(0x14fc748, 0x15eaa60, 0xc00ad321c0, 0xc000044600)
	/snap/go/3129/src/net/http/server.go:1964 +0x44
net/http.(*ServeMux).ServeHTTP(0x2009760, 0x15eaa60, 0xc00ad321c0, 0xc000044600)
	/snap/go/3129/src/net/http/server.go:2361 +0x127
net/http.serverHandler.ServeHTTP(0xc0000ec820, 0x15eaa60, 0xc00ad321c0, 0xc000044600)
	/snap/go/3129/src/net/http/server.go:2741 +0xab
net/http.(*conn).serve(0xc0006448c0, 0x15eba60, 0xc00067dfc0)
	/snap/go/3129/src/net/http/server.go:1847 +0x646
created by net/http.(*Server).Serve
	/snap/go/3129/src/net/http/server.go:2851 +0x2f5

On v1.0.11, the query response for the first query is empty:

{
  "data": {
    "data": []
  }
}

And for the latter query (v1.0.11):

{
  "errors": [
    {
      "code": "ErrorInvalidRequest",
      "message": "Wrong use of var() with [{cnt 2}]."
    }
  ],
  "data": null
}

[srfrog]

Seems to be due to a missing field map init. I've linked the PR fix.
And both queries should return empty since 1.0.12

{
  "data": {
    "data": []
  }
}