Duplicate search results cause search to fail

Summary

When searching for a specific keyword an error page appears with this message:

Oops - an error has occurred
Cause
java.lang.IllegalArgumentException: duplicate key: com.atlassian.confluence.search.v2.ProjectedSearchResult@87d75330
    at com.google.common.base.Preconditions.checkArgument(Preconditions.java:115)

If you run a content index, you will also see the index hang at 99%.

Environment

• Confluence 6.0.0-OD-2015.50.1-0003

Steps to Reproduce

1. Search for keyword in the Confluence search bar at the top navigation panel or through advanced search.
   OR
2. Run a content index of the Confluence instance.

Expected Results

1. The search populates the results of the keyword search.
   OR
2. The content index completes to 100%.

Actual Results

1. You see the following appear on the search page:

   Oops - an error has occurred
   Stack Trace:[hide]
   java.lang.IllegalArgumentException: duplicate key: com.atlassian.confluence.search.v2.ProjectedSearchResult@87d75330
   	at com.google.common.base.Preconditions.checkArgument(Preconditions.java:115)
   	at com.google.common.collect.RegularImmutableMap.<init>(RegularImmutableMap.java:72)
   	at com.google.common.collect.ImmutableMap$Builder.fromEntryList(ImmutableMap.java:245)
   	at com.google.common.collect.ImmutableMap$Builder.build(ImmutableMap.java:231)
   	at com.atlassian.confluence.plugins.cql.impl.factory.SearchResultsFactory.buildFrom(SearchResultsFactory.java:166)
   	at com.atlassian.confluence.plugins.cql.impl.DefaultCQLSearchService.search(DefaultCQLSearchService.java:140)
   	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   	at java.lang.reflect.Method.invoke(Method.java:497)
   	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:302)
   	at org.eclipse.gemini.blueprint.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:56)
   	at org.eclipse.gemini.blueprint.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:60)
   	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
   	at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:133)
   	at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:121)
   	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
   	at org.eclipse.gemini.blueprint.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:70)
   	at org.eclipse.gemini.blueprint.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:53)
   	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
   	at org.eclipse.gemini.blueprint.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:57)
   	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
   	at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:133)
   	at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:121)
   	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
   	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
   	at com.sun.proxy.$Proxy844.search(Unknown Source)
   

   OR
   2. The index hangs at 99% and the below exception is thrown in the confluence log file:

   2015-12-10 11:51:11,898 ERROR [Indexer: 1] [atlassian.bonnie.search.BaseDocumentBuilder] lambda$extractWithLuceneExtractors$120 Error extracting search fields from page: PAGE NAME HERE (25329733) using BackwardsCompatibleExtractor wrapping com.atlassian.confluence.search.lucene.LabelExtractor@13003f0 (confluence.extractors.core:labelExtractor): Failed to lazily initialize a collection
   

Workaround

A Rebuild the content indexes from scratch in some cases fixes the problem.