MySql + EF 6 GroupBy cause NullReferenceException - mysql

Question

After migration from MSSQL to the MySql I faced this issue with some queries.
Packets - .Net 4.8, EF 6.4.4, MySql.Data 8.0.22, MySql.Data.EntityFramework 8.0.22
For example, this query with GroupBy statement caused NRE:
var finalActivities = from examActivity in activitiesFilteredForReport
orderby examActivity.CreateTime descending
group examActivity by axamActivity.CreateTime into gr
select gr.FirstOrDefault();
Exception StackTrace:
System.NullReferenceException: Object reference not set to an instance of an object.
at MySql.Data.EntityFramework.CaseFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.CaseFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.BinaryFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.BinaryFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.BinaryFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.BinaryFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.BinaryFragment.Accept(SqlFragmentVisitor visitor)
at MySql.Data.EntityFramework.SelectGenerator.Visit(DbApplyExpression expression)
at MySql.Data.EntityFramework.SqlGenerator.VisitInputExpression(DbExpression e, String name, TypeUsage type)
at MySql.Data.EntityFramework.SelectGenerator.HandleJoinExpression(DbExpressionBinding left, DbExpressionBinding right, DbExpressionKind joinType, DbExpression joinCondition)
at MySql.Data.EntityFramework.SelectGenerator.Visit(DbJoinExpression expression)
at MySql.Data.EntityFramework.SqlGenerator.VisitInputExpression(DbExpression e, String name, TypeUsage type)
at MySql.Data.EntityFramework.SelectGenerator.VisitInputExpressionEnsureSelect(DbExpression e, String name, TypeUsage type)
at MySql.Data.EntityFramework.SelectGenerator.Visit(DbFilterExpression expression)
at MySql.Data.EntityFramework.SqlGenerator.VisitInputExpression(DbExpression e, String name, TypeUsage type)
at MySql.Data.EntityFramework.SelectGenerator.VisitInputExpressionEnsureSelect(DbExpression e, String name, TypeUsage type)
at MySql.Data.EntityFramework.SelectGenerator.Visit(DbProjectExpression expression)
at MySql.Data.EntityFramework.SelectGenerator.GenerateSQL(DbCommandTree tree)
at MySql.Data.MySqlClient.MySqlProviderServices.CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree)
at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition..ctor(DbProviderFactory storeProviderFactory, DbCommandTree commandTree, DbInterceptionContext interceptionContext, IDbDependencyResolver resolver, BridgeDataReaderFactory bridgeDataReaderFactory, ColumnMapFactory columnMapFactory)
at System.Data.Entity.Core.EntityClient.Internal.EntityProviderServices.CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree, DbInterceptionContext interceptionContext)
at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.CreateCommandDefinition(ObjectContext context, DbQueryCommandTree tree)
at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.Prepare(ObjectContext context, DbQueryCommandTree tree, Type elementType, MergeOption mergeOption, Boolean streaming, Span span, IEnumerable`1 compiledQueryParameters, AliasGenerator aliasGenerator)
at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass41_0.<GetResults>b__1()
at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass41_0.<GetResults>b__0()
at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__31_0()
at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
at System.Linq.Lookup`2.Create[TSource](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
at System.Linq.GroupedEnumerable`3.GetEnumerator()
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
But if I write code like this:
var finalActivities = from examActivity in activitiesFilteredForReport
orderby examActivity.CreateTime descending
group examActivity by axamActivity.CreateTime into gr
select gr.FirstOrDefault().Id;
It gives me Ids without any exception.
In this case, I apply some workaround to make code work:
var ids = activitiesFilteredForReport.GroupBy(activity => activity.OrderExamId)
.Select(g => g.FirstOrDefault().Id);
var finalActivities = from examActivity in activitiesFilteredForReport
join id in ids on examActivity.Id equals id
orderby examActivity.CreateTime descending
select examActivity;
But I not sure is it a good solution. Can anyone help me to sort this issue? What I do wrong?