We are running 9.4.11 of Dynamicweb. Periodically, this error is generated when the product index runs. The product index runs every 15 minutes. Today, it has failed with this error 7 times.
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Status>
<StartTime Ticks="636657102006405167" Humanized="2018-06-27 15:30:00" />
<EndTime Ticks="636657102006561369" Humanized="2018-06-27 15:30:00" />
<Runtime>15</Runtime>
<Count>0</Count>
<TotalCount>0</TotalCount>
<State>Failed</State>
<Fail>
<Reason>The task 'rebuild index.task' failed.</Reason>
<ExceptionMessage>Object reference not set to an instance of an object.</ExceptionMessage>
<ExceptionStackTrace> at Dynamicweb.Ecommerce.Products.ProductRelatedGroup.GetRelatedGroupCollection(String query)
at Dynamicweb.Ecommerce.Common.Application.GetRelatedGroups()
at Dynamicweb.Ecommerce.Indexing.ProductIndexSchemaExtender.GetFields()
at Dynamicweb.Indexing.Schemas.ExtensionFieldDefinition.GetFields()
at Dynamicweb.Indexing.IndexHelper.ConvertToIndex(XElement obj)
at Dynamicweb.Indexing.IndexService.LoadIndex(String name)
at Dynamicweb.Indexing.IndexHelper.BuildIndexInstances(String repository, String indexName, String buildName)
at Dynamicweb.Indexing.Repositories.Tasks.Task.<>c__DisplayClass37_0.<Run>b__0(Tracker tracker)</ExceptionStackTrace>
</Fail>
<LogInformation>Failed.</LogInformation>
<Meta />
</Status>
Not everytime, but sometimes, this failure breaks both indexes and No Products Found is returned until the index is run manually to correct.