Building a graph with an empty map throws a nullpointer exception

[sovelten]

To reproduce:

(graph/digraph {})

It should instead return an empty BasicEditableDigraph record.

[metametadata]

There's a similar issue when passing records into the constructor:

(defrecord Rec [x])

(loom.graph/digraph (Rec. :a))

Exception:

IllegalArgumentException Don't know how to create ISeq from: clojure.lang.Keyword
	clojure.lang.RT.seqFrom (RT.java:557)
	clojure.lang.RT.seq (RT.java:537)
	clojure.core/seq--5467 (core.clj:139)
	clojure.core/seq--5467 (core.clj:139)
	loom.graph/build-graph/build--20106/iter--20158--20164/fn--20165/iter--20160--20169/fn--20170 (graph.cljc:503)
	clojure.lang.LazySeq.sval (LazySeq.java:42)
	clojure.lang.LazySeq.seq (LazySeq.java:51)
	clojure.lang.RT.seq (RT.java:535)
	clojure.core/seq--5467 (core.clj:139)
	clojure.core/seq--5467 (core.clj:139)
	loom.graph/build-graph/build--20106/iter--20158--20164/fn--20165 (graph.cljc:503)
	clojure.lang.LazySeq.sval (LazySeq.java:42)