Allow existing singleton function to be called w/o credentials to return...

[adam-patterson]

... existing instance

@robotpony

[ghost]

Looks good once exception is moved here.

[adam-patterson]

Any exception caused by a failed connection attempt is already handled in the _instance function. The call to the constructor will throw a PDOException if the attempt to connect to the requested database fails. This is then caught and rethrown wrapped in our own exception.

In the case where the instance is null when the function is called, it would just make the connection.

I will change the exception throwing in the two core classes to use asserts instead.

[ghost]

:+1: