.NetCore 5, EF 5: Exceptionm in SqlNullabilityProcessor (no replies)

Hello,
1) i´m using "MySql.EntityFrameworkCore 5.0.5"and "Microsoft.EntityFrameworkCore".
2) following is a Model-Class "Customer"
public class Customer
{
[Key]
public int Key { get; set; }
public string Lastname { get; set; }
}
3) following is a Context-Class:
public class DataContext:DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{

optionsBuilder.UseMySQL(connectionString: @"server=localhost;database=Test;uid=xyz;password=abcd;SSL mode=none");
}

public DataContext()
{

}
public DbSet<Customer> Customers { get; set; }
}

3) i want to execute this code:
DataContext ctx = new DataContext();
string test = "test";
List<Customer> customers=ctx.Customers.Where(m => m.Lastname.StartsWith(test)).ToList();

On executing the öast error i get the exception:
Unhandled expression '[Microsoft.EntityFrameworkCore.Query.SqlExpressions.SqlParameterExpression] COLLATE utf8mb4_bin' of type 'MySql.EntityFrameworkCore.Query.Expressions.Internal.MySQLCollateExpression' encountered in 'SqlNullabilityProcessor'.

with the stacktrace:
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitCustomSqlExpression(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlFunction(SqlFunctionExpression sqlFunctionExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlFunction(SqlFunctionExpression sqlFunctionExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlBinary(SqlBinaryExpression sqlBinaryExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlBinary(SqlBinaryExpression sqlBinaryExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlBinary(SqlBinaryExpression sqlBinaryExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlBinary(SqlBinaryExpression sqlBinaryExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.VisitSqlBinary(SqlBinaryExpression sqlBinaryExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean preserveNonNullableColumns, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SqlExpression sqlExpression, Boolean allowOptimizedExpansion, Boolean& nullable)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Visit(SelectExpression selectExpression)
at Microsoft.EntityFrameworkCore.Query.SqlNullabilityProcessor.Process(SelectExpression selectExpression, IReadOnlyDictionary`2 parameterValues, Boolean& canCache)
at Microsoft.EntityFrameworkCore.Query.RelationalParameterBasedSqlProcessor.ProcessSqlNullability(SelectExpression selectExpression, IReadOnlyDictionary`2 parametersValues, Boolean& canCache)
at Microsoft.EntityFrameworkCore.Query.RelationalParameterBasedSqlProcessor.Optimize(SelectExpression selectExpression, IReadOnlyDictionary`2 parametersValues, Boolean& canCache)
at Microsoft.EntityFrameworkCore.Query.Internal.RelationalCommandCache.GetRelationalCommand(IReadOnlyDictionary`2 parameters)
at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.InitializeReader(DbContext _, Boolean result)
at MySql.EntityFrameworkCore.Storage.Internal.MySQLExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at EF5CoreTest.Program.Main(String[] args) in D:\Temp\obi\EF5CoreTest\EF5CoreTest\Program.cs:line 14


This works with .NetCore 5.0 and MySql.EntityFrameworkCore 3.1.14.

can anyone help?

best regards