SET NAMES utf8mb4;

ALTER TABLE user_verifications
  ADD COLUMN document_hash BINARY(32) NULL AFTER document_mask,
  ADD COLUMN evidence_json TEXT NULL AFTER document_hash,
  ADD KEY idx_user_verifications_document (document_hash);

UPDATE user_verifications SET evidence_json='[]' WHERE evidence_json IS NULL OR evidence_json='';

ALTER TABLE user_verifications
  MODIFY COLUMN evidence_json TEXT NOT NULL;