Uncaught TypeError: this.db.approximateSize is not a function

[pjain01]

@mcollina

Getting this exception:
Uncaught TypeError: this.db.approximateSize is not a function
at DB.approximateSize (index.js:83)
at deferred-leveldown.js:23
at Array.forEach ()
at deferred-leveldown.js:22
at abstract-leveldown.js:33
at abstract-leveldown.js:33
at IDBOpenDBRequest.req.onsuccess (index.js:46)

var level = require('level');
var levelgraph = require("levelgraph");
var db = levelgraph( level('newDB' ) ) ;

db.put( [{
subject: "matteo",
predicate: "friend",
object: "daniele"
}, {
subject: "daniele",
predicate: "friend",
object: "matteo"
},
works fine but when I try to use
db.nav("matteo").archIn("friend").archOut("friend").
solutions(function(err, results) {
console.log(results);
});

I get this exception.

I am using latest level and level-graph.
"dependencies": {
..................
"level": "^5.0.0-0",
"level-js": "^4.0.0",
"levelgraph": "^2.1.1",
.....
}

For now I could get it working(I can see correct output) by commenting out code in "node_modules\encoding-down\index.js":
// DB.prototype.approximateSize = function (start, end, opts, cb) {
// start = this.codec.encodeKey(start, opts)
// end = this.codec.encodeKey(end, opts)
// return this.db.approximateSize(start, end, opts, cb)
// }

but I am not fully sure whether this is a right way to do ??

As per my understanding from various of posts , "db.approximateSize" has been moved to leveldown and so is not part of level-js and hence commenting it out is correct.

Can you please suggest the correct wayout ?