java.lang.NullPointerException: null in Riemann - logstash

Question

I have installed riemann-0.2.13-1.noarch as RPM service. I am sending the events from logstash 5.2.1 and the plugin I have installed is logstash-output-riemann-3.0.0 I wrote the below riemann code to trigger an email. I am getting exception. Please point me where I am going wrong.
Riemann Config:
(let [email (mailer {:host "XXXXX"
:port 25
:subject (fn [events] "Consecutive login failed")
:body (fn [events] "Hello Team, \n \n There are more consecutive logins failure occured #" (riemann.common/time-at (:timestamp event))"")
:from "XXXX"})]
(streams
;Check for every 120sec events
(fixed-time-window
120
(smap
(fn [events]
(let [count-of-failures (count (filter #(re-find #"com.thed.server.access.Exception. Please reset credentials for user. Last error occurred was:Authentication failed, please check user credentials*" (:message %)) events))] ;Calculate the count for matched value
(event
{:status "Class failures"
:metric count-of-failures
:total-fail (> count-of-failures 1)})))
(where (and (= (:status event) "Class failures")
(:total-fail event))
(rollup 1 120
(email "xxx","xxx","xxx")
))prn))))
Error:
WARN [2017-07-06 17:45:49,204] defaultEventExecutorGroup-2-1 - riemann.streams - riemann.streams$smap$stream__6639#55d73fdc threw
java.lang.NullPointerException: null
at java.util.regex.Matcher.getTextLength(Matcher.java:1283)
at java.util.regex.Matcher.reset(Matcher.java:309)
at java.util.regex.Matcher.<init>(Matcher.java:229)
at java.util.regex.Pattern.matcher(Pattern.java:1093)
at clojure.core$re_matcher.invokeStatic(core.clj:4674)
at clojure.core$re_find.invokeStatic(core.clj:4716)
at clojure.core$re_find.invoke(core.clj:4716)
at riemann.config$eval88$fn__93$fn__94.invoke(riemann.config:48)
at clojure.core$filter$fn__4812.invoke(core.clj:2708)
at clojure.lang.LazySeq.sval(LazySeq.java:40)
at clojure.lang.LazySeq.seq(LazySeq.java:49)
at clojure.lang.RT.seq(RT.java:521)
at clojure.lang.RT.countFrom(RT.java:625)
at clojure.lang.RT.count(RT.java:618)
at riemann.config$eval88$fn__93.invoke(riemann.config:48)
at riemann.streams$smap$stream__6639.invoke(streams.clj:161)
at riemann.streams$fixed_time_window_fn$stream__6889$fn__6922.invoke(streams.clj:374)
at riemann.streams$fixed_time_window_fn$stream__6889.invoke(streams.clj:374)
at riemann.core$stream_BANG_$fn__8578.invoke(core.clj:19)
at riemann.core$stream_BANG_.invokeStatic(core.clj:18)
at riemann.core$stream_BANG_.invoke(core.clj:14)
at riemann.transport$handle.invokeStatic(transport.clj:171)
at riemann.transport$handle.invoke(transport.clj:165)
at riemann.transport.tcp$tcp_handler.invokeStatic(tcp.clj:95)
at riemann.transport.tcp$tcp_handler.invoke(tcp.clj:88)
at riemann.transport.tcp$gen_tcp_handler$fn__11550.invoke(tcp.clj:66)
at riemann.transport.tcp.proxy$io.netty.channel.ChannelInboundHandlerAdapter$ff19274a.channelRead(Unknown Source)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:372)
at io.netty.channel.AbstractChannelHandlerContext.access$600(AbstractChannelHandlerContext.java:38)
at io.netty.channel.AbstractChannelHandlerContext$7.run(AbstractChannelHandlerContext.java:363)
at io.netty.util.concurrent.DefaultEventExecutor.run(DefaultEventExecutor.java:66)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:877)
at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)
at java.lang.Thread.run(Thread.java:745)
Whenever I use
(let [count-of-failures (count (filter #(re-find #"com.thed.server.access.Exception. Please reset credentials for user. Last error occurred was:Authentication failed, please check user credentials*" (:message %)) events))].
It throws me above exception but when I use the
(let [count-of-failures (count (filter #(= "com.thed.server.access.Exception. Please reset credentials for user. Last error occurred was:Authentication failed, please check user credentials" (:message %)) events))].
Its sending an email