c.o.s.bitbucket.ScriptedMergeCheck Script merge check failed: PR:

[ashok_projects]

I have implemented MergeChecks by using script runner plugin in bitbucket ,but later i'm facing the below ERROR  in the log file , may I know what might be the issue ,

2019-05-06 18:27:29,268 ERROR [JenkinsWebhook:thread-1627] c.o.s.bitbucket.ScriptedMergeCheck *************************************************************************************
2019-05-06 18:27:29,271 ERROR [JenkinsWebhook:thread-1627] c.o.s.bitbucket.ScriptedMergeCheck Script merge check failed: PR: 2617, repository: fi, file: null
javax.script.ScriptException: javax.script.ScriptException: java.lang.NullPointerException
at org.codehaus.groovy.jsr223.GroovyScriptEngineImpl.eval(GroovyScriptEngineImpl.java:162)
at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:233)
at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoCachedMethodSite.invoke(PojoMetaMethodSite.java:192)
at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:136)
at com.onresolve.scriptrunner.canned.bitbucket.util.BitbucketConditionUtils.processConditionInternal(BitbucketConditionUtils.groovy:141)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at org.codehaus.groovy.runtime.callsite.StaticMetaMethodSite.invoke(StaticMetaMethodSite.java:46)
at org.codehaus.groovy.runtime.callsite.StaticMetaMethodSite.callStatic(StaticMetaMethodSite.java:102)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:233)
at com.onresolve.scriptrunner.canned.bitbucket.util.BitbucketConditionUtils.processConditionSecurely(BitbucketConditionUtils.groovy:117)
at com.onresolve.scriptrunner.canned.bitbucket.util.BitbucketConditionUtils$processConditionSecurely.call(Unknown Source)
at com.onresolve.scriptrunner.bitbucket.ScriptedMergeCheck$_preUpdate_closure3.doCall(ScriptedMergeCheck.groovy:61)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:264)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
at groovy.lang.Closure.call(Closure.java:418)

Getting 4 ERRORS in a day for different PR's