Fix missing None handling of Table.prefixes

[kasium]

Resolves https://github.com/sqlalchemy/alembic/issues/867

Description

Table misses a None handling of prefixes

Checklist

This pull request is:

• A documentation / typographical error fix
  • Good to go, no issue or tests are needed
• A short code fix
  • please include the issue number, and create an issue if none exists, which
    must include a complete example of the issue. one line code fixes without an
    issue and demonstration will not be accepted.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests. one line code fixes without tests will not be accepted.
• A new feature implementation
  • please include the issue number, and create an issue if none exists, which must
    include a complete example of how the feature would look.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests.

Have a nice day!

[sqla-tester]

OK, this is sqla-tester setting up my work on behalf of CaselIT to try to get revision 0638723 of this pull request into gerrit so we can run tests and reviews and stuff

[sqla-tester]

New Gerrit review created for change 0638723: https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/2893

[sqla-tester]

OK, this is sqla-tester setting up my work on behalf of CaselIT to try to get revision b79aca0 of this pull request into gerrit so we can run tests and reviews and stuff

[sqla-tester]

Patchset b79aca0 added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/2893

[kasium]

@CaselIT can you please take a look into the test errors. They seem to be unrelated to my change
DatabaseError: (cx_Oracle.DatabaseError) ORA-12519: TNS:no appropriate service handler found

[CaselIT]

sure, no problem. Mike probably needs to reboot oracle :)

[zzzeek]

when CI is quiet today I'll rebuild all the MSSQL and Oracle containers

[kasium]

thanks :-)

[sqla-tester]

Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/2893 has been merged. Congratulations! :)