Adding a school with no performance data to a comparison made every
school's trend line disappear until that school was removed.
Root cause: /api/compare returns such a school with a single phantom
yearly_data row (the dim_school LEFT JOIN) whose year is null. In
buildCompareChart, Math.trunc(null) is 0, so the axis was seeded at
year 0; fillAcademicYears then walked 0, 101, 202, … and hit its
50-step cap long before reaching the real years, leaving every
school's series mapped entirely to null.
Fix: ignore yearly rows without a real numeric year when building the
axis and the per-school year map. Regression test added.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
