fix: resolve empty enrollment history entries (#64)

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## Description
Fixed the issue where the enrollment history endpoint was returning
entries for terms without enrollment data. Now, the endpoint only
returns entries for terms with actual enrollment data, ensuring that
each entry has at least one data point.
<!--- Describe your changes in detail -->

## Related Issue
This pull request addresses issue
[#31](#31).
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issue first -->
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## Motivation and Context

<!--- Why is this change required? What problem does it solve? -->
This change is required to prevent unintentional behavior in consumers
of the enrollment history endpoint. By ensuring that only terms with
enrollment data are returned, we avoid empty data arrays that could
cause issues or unexpected behavior in downstream applications.
## How Has This Been Tested?

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to -->
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Tested on a local deployment by using the pnpm environment. Minor
changes. None affects other code.
## Screenshots (if appropriate):
Before(includes the empty data sections):
<img width="1383" alt="Screenshot 2025-01-06 at 09 54 58"
src="https://github.com/user-attachments/assets/43f04f6d-ac2b-4f57-affd-921d516f50c6"
/>
After(removed the empty data sections):
<img width="1394" alt="Screenshot 2025-01-06 at 09 55 21"
src="https://github.com/user-attachments/assets/6e84ab49-7552-4da5-b130-bc398c7a3862"
/>

## Types of changes

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the boxes that apply: -->

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

## Checklist:

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that apply. -->
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here to help! -->

- [ ] My code involves a change to the database schema.
- [ ] My code requires a change to the documentation.

---------

Co-authored-by: Eddy Chen <[email protected]>

apps/api/src/services/enrollment-history.ts

@@ -159,8 +159,11 @@ export class EnrollmentHistoryService {
         section.statusHistory.push(row.status ?? "");
       }
     }
-    return transformedSectionRows
-      .values()
+    const filteredSections = transformedSectionRows.values().filter((section) => {
+      return section.dates.length > 0;
+    });
+
+    return filteredSections
       .map(({ instructors, meetings, ...rest }) => ({
         instructors: Array.from(instructors),
         meetings: meetings.map(({ bldg, ...rest }) => ({ bldg: Array.from(bldg), ...rest })),