The `NullReferenceException` type is intended to only be thrown by the CLR.
In most cases, it should be converted to an `ArgumentException` or an
`InvalidOperationException`, depending on if the null value is a parameter
to the current method or not.
The `Exception` type should never really be thrown as it doesn't provide any
additional information or hints as to the issue. It also forces users that
would like to handle expected exceptions to catch all exceptions. These are
converted to an exception type that more accurately describes the reason for
raising the exception: `KeyNotFoundException`, `InvalidOperationException`
- Adding `LazyToUpper()` implementation, that will avoid the call to
`ToUpper` if the string is already upper.
- Reduce the timezone conversions at `Time.EachTradeableDayInTimeZone`
- `TotalPortfolioValue` will iterate over all securities once
- Adding new `SecurityIdentifier` cache, significant impact for
algorithms using coarse/fine data
Martin Molinero