java.lang.UnsupportedOperationException: Unknown Collection type

No clear idea what's going on here:

```
Exception in thread "main" java.lang.Exception: Couldn't eval form (...)
(defn cut-stream-on-flag [stream flag]
  "returns a lazy sequence which wraps the passed in stream. Each
   time an element is taken, we check flag. If flag is false, we
   end the sequence.\n\n   Basically the idea is that this will turn an infinite (usually
   io-bound) sequence into a finite one which ends when we say it
   ends."
  (lazy-seq (if (and (clojure.core/deref flag) (seq stream))
                  (cons (first stream) (cut-stream-on-flag (rest stream) flag))
                  (quote ()))))

	at cloverage.instrument$instrument$fn__515.invoke(instrument.clj:325)
	at cloverage.instrument$instrument.invoke(instrument.clj:315)
(...)
Caused by: java.lang.UnsupportedOperationException: Unknown Collection type, compiling:(com/loggly/metamorphosis/utils.clj:26)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6462)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyze(Compiler.java:6223)
	at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:5618)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6455)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6443)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyze(Compiler.java:6223)
	at clojure.lang.Compiler$NewExpr$Parser.parse(Compiler.java:2478)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6455)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyze(Compiler.java:6223)
	at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:5618)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6455)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6443)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyze(Compiler.java:6223)
	at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:5618)
	at clojure.lang.Compiler$FnMethod.parse(Compiler.java:5054)
	at clojure.lang.Compiler$FnExpr.parse(Compiler.java:3674)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6453)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6443)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.access$100(Compiler.java:37)
	at clojure.lang.Compiler$DefExpr$Parser.parse(Compiler.java:518)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6455)
	at clojure.lang.Compiler.analyze(Compiler.java:6262)
	at clojure.lang.Compiler.analyze(Compiler.java:6223)
	at clojure.lang.Compiler.eval(Compiler.java:6515)
	at clojure.lang.Compiler.eval(Compiler.java:6501)
	at clojure.lang.Compiler.eval(Compiler.java:6477)
	at clojure.core$eval.invoke(core.clj:2797)
	at cloverage.instrument$instrument$fn__515$fn__516.invoke(instrument.clj:318)
	at cloverage.instrument$instrument$fn__515.invoke(instrument.clj:316)
	... 20 more
Caused by: java.lang.UnsupportedOperationException: Unknown Collection type
	at clojure.lang.Compiler$EmptyExpr.emit(Compiler.java:2730)
	at clojure.lang.Compiler$BodyExpr.emit(Compiler.java:5662)
	at clojure.lang.Compiler$IfExpr.doEmit(Compiler.java:2593)
	at clojure.lang.Compiler$IfExpr.emit(Compiler.java:2544)
	at clojure.lang.Compiler$BodyExpr.emit(Compiler.java:5662)
	at clojure.lang.Compiler$BodyExpr.emit(Compiler.java:5662)
	at clojure.lang.Compiler$FnMethod.doEmit(Compiler.java:5215)
	at clojure.lang.Compiler$FnMethod.emit(Compiler.java:5069)
	at clojure.lang.Compiler$FnExpr.emitMethods(Compiler.java:3600)
	at clojure.lang.Compiler$ObjExpr.compile(Compiler.java:4233)
	at clojure.lang.Compiler$FnExpr.parse(Compiler.java:3732)
	at clojure.lang.Compiler.analyzeSeq(Compiler.java:6453)
	... 56 more
```