Improve error handling for keyless entities in MetadataProvider

Author: fabien.menager

src/PhenX.EntityFrameworkCore.BulkInsert/Metadata/MetadataProvider.cs

@@ -34,11 +34,11 @@ public TableMetadata GetTableInfo<T>(DbContext context)
                 throw new InvalidOperationException($"The type '{modelType.FullName}' is not part of the model for the current context.");
             }
 
-
             // Filter out entities without an associated table
             // See also https://learn.microsoft.com/en-us/ef/core/modeling/keyless-entity-types
             if (entityType.GetTableName() is null)
             {
+                throw new InvalidOperationException($"The type '{modelType.FullName}' is not mapped to a table in the database or is keyless.");
             }
 
             var provider = context.GetService<IBulkInsertProvider>();