COD fails to complete (BE bugfix)

**Describe the bug in current situation**
Filer fails to complete change of directors if there is a director being changed without a middle name

**Impact of this bug**
COD fails to complete.

**Chance of Occurring (high/medium/low/very low)**
High

**Pre Conditions: which Env, any pre-requesites or assumptions to execute steps?**
Changing a director with no middle name

**Fix**: Either UI or Filer/verify colin-api
**Sentry Error:** https://sentry.io/organizations/registries/issues/2021872848/?project=1533020&query=is%3Aunresolved

**Notes:**
- per Thor, having null middle names is valid (current schema is correct)
- even though the Filings UI will no longer send null officer middle names (#5622), ultimately other API users may do so
- therefore, this ticket is to fix the BE to handle this