This is being done in an effort to prevent symbol collisions within the
custom data (SecurityType.Base) namespace. The custom data type's name,
is used for disambiguation. As written, this change will break several
user algorithms that still rely on using the implicit string -> Symbol
lift. Providing this type information is optional an currently only being
used by AddData<T> methods. Other consumers of SecurityType.Base symbols
arn't at risk for collision, such as the UserDefinedUniverse, ScheduledUniverse
and others that are LEAN controlled. In order to maintain backwards compatibility,
the SymbolCache was updated to do a hard search when the requested ticker was
not found, looking for the prefix ('ticker.').
Fixes#3332
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`
Having a symbol implicit to string and then string to symbol must be
inverse operations, consider the case we pass Symbol data.Symbol to a
method expecting a string, and then that same method invokes another
method expecting a Symbol, we'll need it to resolve back to the original
symbol.
Michael Handschuh