Raised when a field's declared normalizer could not produce a normalized value (ADR-0003's exception table, the "a host normalizer raises or returns a non-binary" row).

The built-in normalizers never reach this exception. They are total on every binary by construction - Encryptor.Ecto.BlindIndex.Normalizer says how - so every condition reported here is either a {module, function} normalizer the host supplied misbehaving, or a value that is not a binary arriving where one was required.

What it names, and what it cannot name

The common fields carry the encrypted field's declared table and column, and :index_name names which of a column's indexes was being computed. That is deliberately the whole identification: ADR-0003 decision 4 says the exception names the table and column and no value, and the value in hand at the moment a normalizer fails is a plaintext.

So the plaintext is absent, and so is anything derived from it. In particular a rescued exception's message is not carried - a host normalizer that raises ArgumentError on the value it was handed usually puts that value in the message, which would smuggle the plaintext into this exception through the one field that looks safe to copy. :reason carries the rescued exception's module and nothing else.

:normalizer is the declaration's own :normalize option: an atom, or the {module, function} pair the host wrote. Both are names from the schema line, which is what makes the failure findable.