[quinnj]

Depends on #26; its row-input and CI foundation is included until that PR merges. The additional change covers the JSON object-of-arrays path.

An empty first column currently disables equal-length validation: {"a":[],"b":[1]} is accepted even though its columns have different lengths. Recognize the first column using the existing column-name count so zero remains a valid initialized length.

An entirely null column also throws UndefVarError because the union method does not bind its type parameter for Nothing. Handle that exact type as Missing. Empty parsed arrays can have Union{} as their element type; use Any for those unknown column types so constructing a table schema and converting the empty table succeeds on current Julia. Populated and mixed-null column types retain their existing handling.

Validation:

• The preceding column-length probe has eight passes and four failures, including accepted unequal lengths after an empty first column. Two all-null schema checks separately error with the unbound type parameter. Current Julia also reproduces empty-column schema/row/column conversion errors before the empty-type fallback.
• All 46 new public checks pass: unequal lengths in both orders and after multiple empty columns, valid equal empty/populated columns, mixed nulls, all-null columns through text/byte/IO/parsed inputs, schema types, and row/column conversions.
• The full 140-check suite passes on Julia 1.6.7 and 1.13.0 with four threads and forced bounds checks. git diff --check passes.
• All six checks pass at 7d72b625be0d176313a65d913c3dedfb1291b03e: all four native jobs in run 37186035745, including Julia 1.0, plus both Codecov checks. All four coverage sessions were accepted at the correct repository/commit destination; the stable job uploaded 893 bytes and the final report is 93.75%. Merge remains held for prerequisite Restore JSON row inputs and missing fields after empty rows #26 and the required independent approval.

Co-authored by Codex

AI disclosure: This work was prepared with assistance from OpenAI Codex.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.75%. Comparing base (fea5d94) to head (b98b669).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
+ Coverage   93.61%   93.75%   +0.13%     
==========================================
  Files           1        1              
  Lines          94       96       +2     
==========================================
+ Hits           88       90       +2     
  Misses          6        6              

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