I am using Datasets as report data sources and date columns get mapped as datetime types in Designer. When the report gets rendered with null date fields, I get the message 'Expression in text property ... can't be evaluated." - this slows down rendering performance dramatically. If the data type gets changed to datetime (nullable) everything works as intended with great performance. I don't know the best way to avoid this.

1) Is there a way to define a .Net data type conversion map? For example, I can set that .Net date columns always get mapped as datetime (nullable).
2) The report engine verifies even datetime types if they are null.
3) After registering the data I loop through the Dictionary and change datetime types to datetime (nullable).
4) Check it in the text property with IIF(). Won't be my 1st choice...
5) Any other approaches?
Thanks a lot in advance.