Unable to convert a simple xls file

[rameshsr]

When I run the command, lein run ./files/demo.xls ./files I am getting the following error.

error :: Converting./files/demo.xlsxfailed with: java.lang.NullPointerException demo.xlsx demo.xlsx

[#<StackTraceElement clojure.core$name.invoke(core.clj:1505)>, #<StackTraceElement excel_to_json.converter$add_sheet_config$fn__4707.invoke(converter.clj:102)>, #<StackTraceElement clojure.lang.ArrayChunk.reduce(ArrayChunk.java:58)>, #<StackTraceElement clojure.core.protocols$fn__6041.invoke(protocols.clj:98)>, #<StackTraceElement clojure.core.protocols$fn__6005$G__6000__6014.invoke(protocols.clj:19)>, #<StackTraceElement clojure.core.protocols$seq_reduce.invoke(protocols.clj:31)>, #<StackTraceElement clojure.core.protocols$fn__6028.invoke(protocols.clj:48)>, #<StackTraceElement clojure.core.protocols$fn__5979$G__5974__5992.invoke(protocols.clj:13)>, #<StackTraceElement clojure.core$reduce.invoke(core.clj:6177)>, #<StackTraceElement excel_to_json.converter$add_sheet_config.invoke(converter.clj:97)>, #<StackTraceElement excel_to_json.converter$parse_normal$iter__4728__4732$fn__4733.invoke(converter.clj:144)>, #<StackTraceElement clojure.lang.LazySeq.sval(LazySeq.java:42)>, #<StackTraceElement clojure.lang.LazySeq.seq(LazySeq.java:60)>, #<StackTraceElement clojure.lang.RT.seq(RT.java:484)>, #<StackTraceElement clojure.core$seq.invoke(core.clj:133)>, #<StackTraceElement clojure.core$dorun.invoke(core.clj:2780)>, #<StackTraceElement clojure.core$doall.invoke(core.clj:2796)>, #<StackTraceElement excel_to_json.converter$parse_normal.invoke(converter.clj:141)>, #<StackTraceElement excel_to_json.converter$parse_workbook$iter__4743__4747$fn__4748.invoke(converter.clj:152)>, #<StackTraceElement clojure.lang.LazySeq.sval(LazySeq.java:42)>, #<StackTraceElement clojure.lang.LazySeq.seq(LazySeq.java:60)>, #<StackTraceElement clojure.lang.RT.seq(RT.java:484)>, #<StackTraceElement clojure.core$seq.invoke(core.clj:133)>, #<StackTraceElement clojure.core$dorun.invoke(core.clj:2780)>, #<StackTraceElement clojure.core$doall.invoke(core.clj:2796)>, #<StackTraceElement excel_to_json.converter$parse_workbook.invoke(converter.clj:149)>, #<StackTraceElement excel_to_json.converter$convert.invoke(converter.clj:155)>, #<StackTraceElement excel_to_json.core$convert_and_save.invoke(core.clj:26)>, #<StackTraceElement excel_to_json.core$run.invoke(core.clj:66)>, #<StackTraceElement excel_to_json.cli$_main.doInvoke(cli.clj:80)>, #<StackTraceElement clojure.lang.RestFn.invoke(RestFn.java:436)>, #<StackTraceElement clojure.lang.Var.invoke(Var.java:423)>, #<StackTraceElement user$eval5.invoke(form-init1702119447777732498.clj:1)>, #<StackTraceElement clojure.lang.Compiler.eval(Compiler.java:6619)>, #<StackTraceElement clojure.lang.Compiler.eval(Compiler.java:6609)>, #<StackTraceElement clojure.lang.Compiler.load(Compiler.java:7064)>, #<StackTraceElement clojure.lang.Compiler.loadFile(Compiler.java:7020)>, #<StackTraceElement clojure.main$load_script.invoke(main.clj:294)>, #<StackTraceElement clojure.main$init_opt.invoke(main.clj:299)>, #<StackTraceElement clojure.main$initialize.invoke(main.clj:327)>, #<StackTraceElement clojure.main$null_opt.invoke(main.clj:362)>, #<StackTraceElement clojure.main$main.doInvoke(main.clj:440)>, #<StackTraceElement clojure.lang.RestFn.invoke(RestFn.java:421)>, #<StackTraceElement clojure.lang.Var.invoke(Var.java:419)>, #<StackTraceElement clojure.lang.AFn.applyToHelper(AFn.java:163)>, #<StackTraceElement clojure.lang.Var.applyTo(Var.java:532)>, #<StackTraceElement clojure.main.main(main.java:37)>] [done]

I am using Leiningen 2.7.1 on Java 1.7.0_79 Java HotSpot(TM) 64-Bit Server VM

Can you please help me get around this problem? Attached the sample xlsx file I am using to reproduce this issue.