Two defects in _build_comparison_conditions, both reachable from any
route that accepts filters:
1. A null operand hit float(None), raising TypeError where only
ValueError was caught — an unhandled 500. A null operand is a null
check, not a value comparison, so {"ne": null} now compiles to
IS NOT NULL and the other operators reject null with a 422. Equality
against null already produced IS NULL via _build_field_condition.
2. Numeric operators float()-cast on every column type, so a string
inequality on a text column ({"session_id": {"ne": "abc"}}) was
rejected as an invalid number. Coercion is now gated on the column
actually being numeric; text columns compare as text. Numeric columns
still validate, and TypeError is caught alongside ValueError.
Existing ne coverage only exercised the JSONB metadata path, which uses
_safe_numeric_cast and handles strings — the scalar column path was
untested. Adds cases for both.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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