Adding datomic-free to project fails cider-nrepl

I’m using Duct/Integrant and want to play with Datomic first as an in-memory database. When I add [com.datomic/datomic-free “0.9.5697”] to my project.clj file, I get the error shown below and cannot connect to cider-nrepl. Can someone give me a hint as to what might be causing this and in which user groups I should ask for help, duct, cider, or piggieback?

error in process sentinel: Could not start nREPL server: Error loading cemerick.piggieback: java.lang.NoSuchMethodError: com.google.common.base.Preconditions.checkState(ZLjava/lang/String;Ljava/lang/Object;)V, compiling:(closure.clj:100:1)
Exception in thread “main” java.lang.RuntimeException: Unable to resolve var: cemerick.piggieback/wrap-cljs-repl in this context, compiling:(/private/var/folders/nk/nz7nrdj95ss2nlvzbhzclsz40000gn/T/form-init3195270554432328219.clj:1:8988)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:7010)
at clojure.lang.Compiler.analyze(Compiler.java:6773)
at clojure.lang.Compiler.analyze(Compiler.java:6729)
at clojure.lang.Compiler$InvokeExpr.parse(Compiler.java:3881)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:7005)
at clojure.lang.Compiler.analyze(Compiler.java:6773)
at clojure.lang.Compiler.analyze(Compiler.java:6729)
at clojure.lang.Compiler$InvokeExpr.parse(Compiler.java:3881)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:7005)
at clojure.lang.Compiler.analyze(Compiler.java:6773)
at clojure.lang.Compiler.access$300(Compiler.java:38)
at clojure.lang.Compiler$LetExpr$Parser.parse(Compiler.java:6368)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:7003)
at clojure.lang.Compiler.analyze(Compiler.java:6773)
at clojure.lang.Compiler.analyze(Compiler.java:6729)
at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:6100)
at clojure.lang.Compiler$FnMethod.parse(Compiler.java:5460)
at clojure.lang.Compiler$FnExpr.parse(Compiler.java:4022)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:7001)
at clojure.lang.Compiler.analyze(Compiler.java:6773)
at clojure.lang.Compiler.eval(Compiler.java:7059)
at clojure.lang.Compiler.eval(Compiler.java:7052)
at clojure.lang.Compiler.load(Compiler.java:7514)
at clojure.lang.Compiler.loadFile(Compiler.java:7452)
at clojure.main$load_script.invokeStatic(main.clj:278)
at clojure.main$init_opt.invokeStatic(main.clj:280)
at clojure.main$init_opt.invoke(main.clj:280)
at clojure.main$initialize.invokeStatic(main.clj:311)
at clojure.main$null_opt.invokeStatic(main.clj:345)
at clojure.main$null_opt.invoke(main.clj:342)
at clojure.main$main.invokeStatic(main.clj:424)
at clojure.main$main.doInvoke(main.clj:387)
at clojure.lang.RestFn.applyTo(RestFn.java:137)
at clojure.lang.Var.applyTo(Var.java:702)
at clojure.main.main(main.java:37)
Caused by: java.lang.RuntimeException: Unable to resolve var: cemerick.piggieback/wrap-cljs-repl in this context
at clojure.lang.Util.runtimeException(Util.java:221)
at clojure.lang.Compiler$TheVarExpr$Parser.parse(Compiler.java:720)
at clojure.lang.Compiler.analyzeSeq(Compiler.java:7003)
… 34 more
Subprocess failed

I was able to fix the problem by adding the following exclusion.
[com.datomic/datomic-free “0.9.5697”
:exclusions [com.google.guava/guava]]