error

~/development/clojure/session(master) $ lein run
Starting database
Starting database
Exception in thread "main" clojure.lang.ExceptionInfo: Error in component :web-server in system session.system.SessionSystem calling #'com.stuartsierra.component/start {:reason :com.stuartsierra.component/component-function-threw-exception, :function #'com.stuartsierra.component/start, :component #session.webserver.WebServer{:ws-chan #<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@233789d9>, :port nil}, :system #session.system.SessionSystem{:system-database #session.datomic.Database{:uri "datomic:free://localhost:4334/session-system3", :connection #<Connection {:db-id "session-system3-c954684a-cbe0-41f1-a540-ae9046a95dc6", :unsent-updates-queue 0, :pending-txes 0, :next-t 1004, :basis-t 1002, :index-rev 0}>, :datomic-process {:out #<ProcessPipeInputStream java.lang.UNIXProcess$ProcessPipeInputStream@138b9abe>, :in #<ProcessPipeOutputStream java.lang.UNIXProcess$ProcessPipeOutputStream@35277c6c>, :err #<ProcessPipeInputStream java.lang.UNIXProcess$ProcessPipeInputStream@7a364e1c>, :process #<UNIXProcess java.lang.UNIXProcess@74cff17c>}, :seed {:data [], :schema [{:db/ident :session/meta, :db/id #db/id[:db.part/db -1000000]} {:db/cardinality :db.cardinality/one, :db.install/_attribute :db.part/db, :db/unique :db.unique/identity, :db/valueType :db.type/uuid, :db/ident :index/id, :db/id #db/id[:db.part/db -1000001]} {:db/cardinality :db.cardinality/one, :db.install/_attribute :db.part/db, :db/valueType :db.type/string, :db/ident :index/name, :db/id #db/id[:db.part/db -1000002]} {:db/cardinality :db.cardinality/one, :db.install/_attribute :db.part/db, :db/valueType :db.type/instant, :db/ident :index/created-at, :db/id #db/id[:db.part/db -1000003]} {:db/cardinality :db.cardinality/one, :db.install/_attribute :db.part/db, :db/valueType :db.type/instant, :db/ident :index/modified-at, :db/id #db/id[:db.part/db -1000004]} {:db/cardinality :db.cardinality/one, :db.install/_attribute :db.part/db, :db/valueType :db.type/ref, :db/ident :index/group, :db/id #db/id[:db.part/db -1000005]} {:db/cardinality :db.cardinality/one, :db.install/_attribute :db.part/db, :db/valueType :db.type/string, :db/ident :index.group/name, :db/id #db/id[:db.part/db -1000006]}]}, :system-base-uri "datomic:free://localhost:4334/"}, :session-database #<Atom@38b0e2a7: nil>, :web-server #session.webserver.WebServer{:ws-chan #<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@233789d9>, :port nil}, :app #session.app.component.SessionApp{:system-database nil, :session-database nil, :web-server nil, :object-mapping nil, :merchant nil}, :merchant #session.io.Merchant{:data-mappings ({:record yantra.datatypes.Slider, :tag "yantra.controls/Slider"} {:record yantra.datatypes.Column, :tag "yantra.layout/Column"} {:record yantra.datatypes.Graphics, :tag "yantra.graphics/Graphics"} {:record yantra.datatypes.Point, :tag "yantra.graphics/Point"} {:record yantra.datatypes.Line, :tag "yantra.graphics/Line"} {:record yantra.datatypes.Disk, :tag "yantra.graphics/Disk"} {:record yantra.datatypes.Rectangle, :tag "yantra.graphics/Rectangle"} {:record yantra.datatypes.Style, :tag "yantra.graphics/Style"} {:record yantra.datatypes.ListLinePlot, :tag "yantra.plot/ListLinePlot"} {:record yantra.datatypes.BarChart, :tag "yantra.plot/BarChart"} {:record yantra.datatypes.HTMLElement, :tag "yantra.dom/HTMLElement"} {:record session.datatypes.Loop, :tag "session/Loop"} {:record session.datatypes.Session, :tag "session/Session"}), :object-mappings {:id-to-object #<Atom@73eae5f: {}>, :object-to-id #<Atom@4902c584: {}>}}}}
	at clojure.core$ex_info.invoke(core.clj:4327)
	at com.stuartsierra.component$try_action.invoke(component.clj:101)
	at com.stuartsierra.component$update_system$fn__310.invoke(component.clj:124)
	at clojure.core.protocols$fn__6037.invoke(protocols.clj:127)
	at clojure.core.protocols$fn__6005$G__6000__6014.invoke(protocols.clj:19)
	at clojure.core.protocols$seq_reduce.invoke(protocols.clj:31)
	at clojure.core.protocols$fn__6028.invoke(protocols.clj:48)
	at clojure.core.protocols$fn__5979$G__5974__5992.invoke(protocols.clj:13)
	at clojure.core$reduce.invoke(core.clj:6177)
	at com.stuartsierra.component$update_system.doInvoke(component.clj:128)
	at clojure.lang.RestFn.invoke(RestFn.java:445)
	at com.stuartsierra.component$start_system.invoke(component.clj:150)
	at session.system.SessionSystem.start(system.clj:14)
	at session.main$_main.invoke(main.clj:14)
	at session.main$_main.invoke(main.clj:9)
	at clojure.lang.Var.invoke(Var.java:411)
	at user$eval5$fn__7.invoke(form-init3153284742641619401.clj:1)
	at user$eval5.invoke(form-init3153284742641619401.clj:1)
	at clojure.lang.Compiler.eval(Compiler.java:6619)
	at clojure.lang.Compiler.eval(Compiler.java:6609)
	at clojure.lang.Compiler.load(Compiler.java:7064)
	at clojure.lang.Compiler.loadFile(Compiler.java:7020)
	at clojure.main$load_script.invoke(main.clj:294)
	at clojure.main$init_opt.invoke(main.clj:299)
	at clojure.main$initialize.invoke(main.clj:327)
	at clojure.main$null_opt.invoke(main.clj:362)
	at clojure.main$main.doInvoke(main.clj:440)
	at clojure.lang.RestFn.invoke(RestFn.java:421)
	at clojure.lang.Var.invoke(Var.java:419)
	at clojure.lang.AFn.applyToHelper(AFn.java:163)
	at clojure.lang.Var.applyTo(Var.java:532)
	at clojure.main.main(main.java:37)
Caused by: java.lang.NullPointerException
	at clojure.lang.RT.intCast(RT.java:1087)
	at ring.adapter.jetty$create_server.invoke(jetty.clj:52)
	at ring.adapter.jetty$run_jetty.invoke(jetty.clj:80)
	at session.webserver.WebServer.start(webserver.clj:29)
	at com.stuartsierra.component$eval252$fn__253$G__244__255.invoke(component.clj:4)
	at com.stuartsierra.component$eval252$fn__253$G__243__258.invoke(component.clj:4)
	at clojure.lang.Var.invoke(Var.java:415)
	at clojure.lang.AFn.applyToHelper(AFn.java:161)
	at clojure.lang.Var.applyTo(Var.java:532)
	at clojure.core$apply.invoke(core.clj:619)
	at com.stuartsierra.component$try_action.invoke(component.clj:98)
	... 30 more