Investigate NODE-4354 - Unable to specify empty readPreferenceTags in a connection string

NODE-4354 Description
According to the docs it should be possible to specify an empty readPreferenceTags, so that we can fallback to all nodes in a replica set. But due to this check it leads to an error.

Steps to reproduce

Use a connection string like this

...&readPreferenceTags=x:y&readPreferenceTags=...