I've followed the steps in

https://our.umbraco.org/forum/umbraco-7/using-umbraco-7/61148-Search-not-returning-expected-results#comment-230133

to create custom analyzer, and setup config files but ended with the following config error on app startup:

Server Error in '/' Application.
Configuration Error

Description: An error occurred during the processing of a
configuration file required to service this request. Please review the
specific error details below and modify your configuration file
appropriately. 

Parser Error Message: Value cannot be null. Parameter name: type

Source Error: 

Line 23:
<add name="ExternalIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine" analyzer="LuceneNetContrib.EnglishSnowballAnalyzer,
LuceneNetContrib"/> 

ExamineSettings.config:

<Examine>
  <ExamineIndexProviders>
      <providers>
          <add name="InternalIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine"
               supportUnpublished="true"
               supportProtected="true"
               analyzer="Lucene.Net.Analysis.WhitespaceAnalyzer, Lucene.Net"/>

          <add name="InternalMemberIndexer" type="UmbracoExamine.UmbracoMemberIndexer, UmbracoExamine"
               supportUnpublished="true"
               supportProtected="true"
               analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net"/>

          <!-- default external indexer, which excludes protected and unpublished pages-->
          <add name="ExternalIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine"
               analyzer="LuceneNetContrib.EnglishSnowballAnalyzer, LuceneNetContrib"/>

          <add name="PDFIndexer" type="UmbracoExamine.PDF.PDFIndexer, UmbracoExamine.PDF"
               analyzer="LuceneNetContrib.EnglishSnowballAnalyzer, LuceneNetContrib"
               extensions=".pdf"
               umbracoFileProperty="umbracoFile"/>
      </providers>
  </ExamineIndexProviders>

  <ExamineSearchProviders defaultProvider="ExternalSearcher">
      <providers>
          <add name="InternalSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine"
               analyzer="Lucene.Net.Analysis.WhitespaceAnalyzer, Lucene.Net"/>

          <add name="ExternalSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine" />

          <add name="InternalMemberSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine"
               analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net" enableLeadingWildcard="true"/>
          <add name="PDFSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine"/>
          <add name="ContentSearcher" type="Examine.LuceneEngine.Providers.MultiIndexSearcher, Examine"
               analyzer="LuceneNetContrib.EnglishSnowballAnalyzer, LuceneNetContrib" enableLeadingWildcards="true" indexSets="ExternalIndexSet,PDFIndexSet"/>
      </providers>
  </ExamineSearchProviders>

</Examine>

ExamineIndex.config:

<ExamineLuceneIndexSets>
    <!-- The internal index set used by Umbraco back-office - DO NOT REMOVE -->
    <IndexSet SetName="InternalIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/Internal/"/>

    <!-- The internal index set used by Umbraco back-office for indexing members - DO NOT REMOVE -->
    <IndexSet SetName="InternalMemberIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/InternalMember/">
        <IndexAttributeFields>
            <add Name="id" />
            <add Name="nodeName"/>
            <add Name="updateDate" />
            <add Name="writerName" />
            <add Name="loginName" />
            <add Name="email" />
            <add Name="nodeTypeAlias" />
        </IndexAttributeFields>
    </IndexSet>

    <!-- Default Indexset for external searches, this indexes all fields on all types of nodes-->
    <IndexSet SetName="ExternalIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/External/" />
    <IndexSet SetName="PDFIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/PDFs"/>
</ExamineLuceneIndexSets>

Can someone please help?

Thanks, Bala