Bug CTHUB - GER/SUVI dataset empty postal code cells causing improper error warning

**Describe the Bug**
An improper system error being shown when uploading a GER/SUVI dataset to CTHUB that contains empty postal code cells.

**Expected Behaviour**
When a GER/SUVI dataset is uploaded to CTHUB, and it contains empty postal code cells, no warning should be issued, as this data column is allowed to have missing values.

**Actual Behaviour**
The user is uploading GER/SUVI datasets with empty postal code cells, and is being issued a warning by the system.

**Implications**
This bug is improperly informing the user about a warning in their data. The 'GER_format_for_CTHub.xlsx" file lists empty postal code cells as acceptable.

**Steps To Reproduce**
Steps to reproduce the behaviour:
User/Role:
1. Go to (https://cthub-dev.apps.silver.devops.gov.bc.ca/upload)
2. Select the "Go Electric Rebates Program" to upload a file
3. Upload the 'no_errors_no_warnings.xlsx" file that contains an empty postal code cell
4. See error

Reproduce the upload at the CTHUB upload page with no_errors_no_warnings.xlsx, comparing it with GER_format_for_CTHub.xlsx. Trace the GER/SUVI postal-code validation used for the Go Electric Rebates Program and identify why an empty cell produces a warning. Done means the file uploads without a warning for an empty postal code cell.

Written by the indexing model from the issue text.