DVT issues an error while doing a column validation involving views.

**Describe the bug**
While trying to do a column validation, DVT reports the following error:
```
Traceback (most recent call last):
File "/home/dvt/venv/lib/python3.11/site-packages/multipledispatch/dispatcher.py", line 269, in __call__
func = self._cache[types]
~~~~~~~~~~~^^^^^^^
KeyError: (, )

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/dvt/venv/bin/data-validation", line 8, in
sys.exit(main())
```

**What version of DVT are you using?**
Ex: 7.1.0

**What type of connections are you using for source and target?**
Postgres vs Postgres.

**Steps to reproduce the behavior**
Ex: 1. Add '...'
2. Execute '....'
3. Scroll down to '....'
4. See error

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**How are you executing DVT?**
Ex: CLI commands on local computer or VM, within a DAG, Cloud Run job, etc

**Additional context**
Add any other context about the problem here.