SeleniumHQ/selenium · warning · Error::SerializationError

#{name}##{field.name} is required but was missing from the r

Error message

#{name}##{field.name} is required but was missing from the response

What it means

A required BiDi Record field was absent from the response. By default (lenient mode) this is only warned and treated as omitted (UNSET), so a schema ahead of the browser does not block callers. With the SE_BIDI_STRICT env var set, the same condition escalates to Error::SerializationError. This keeps required-but-missing distinct from an explicit null.

Source

Thrown at rb/lib/selenium/webdriver/bidi/serialization/record.rb:231

            def fixed?(field)
              !UNSET.equal?(field.fixed)
            end

            def wire_value(field, json_payload)
              return field.fixed if fixed?(field)
              return read(field, json_payload[field.wire_key]) if json_payload.key?(field.wire_key)
              return UNSET unless field.required

              missing_required(field)
            end

            # A required field absent from the response is tolerated as omitted (UNSET) and warned, so a
            # schema ahead of the browser does not block the caller; strict mode (SE_BIDI_STRICT) escalates
            # to an error for callers who want it. Omitted (UNSET) stays distinct from an explicit null (nil),
            # which matters for the required-and-nullable fields the schema flags.
            def missing_required(field)
              message = "#{name}##{field.name} is required but was missing from the response"
              raise Error::SerializationError, message if Serialization.strict?

              WebDriver.logger.warn(message, id: :bidi_missing_required)
              UNSET
            end

            def read(field, raw)
              if raw.nil?
                return raw if field.nullable

                raise Error::SerializationError, "#{name}##{field.name} received null but is not nullable"
              end
              check_shape(field, raw)
              return Serialization.to_symbol("#{name}##{field.name}", raw, enum_hash(field)) if field.enum

              if field.ref.nil?
                check_primitive(field, raw) unless field.list
                return raw
              end

View on GitHub (pinned to aa36b38e69)

Solutions

1. Unset SE_BIDI_STRICT to downgrade to a warning if the missing field is non-critical.
2. Align browser/driver and Selenium versions so the required field is emitted.
3. Filter the :bidi_missing_required warning via WebDriver.logger.ignore(:bidi_missing_required) if intentional.
4. Report the missing-field divergence with the response payload.

Example fix

// before
ENV['SE_BIDI_STRICT'] = '1'
bidi.call(...)
// after
# omit SE_BIDI_STRICT (default lenient), or:
WebDriver.logger.ignore(:bidi_missing_required)

# Avoid enabling strict mode unless you can tolerate hard failures on schema drift.
ENV.delete('SE_BIDI_STRICT') if ENV['SE_BIDI_STRICT'] == '1'

begin
  record = SomeRecord.from_json(payload)
rescue Selenium::WebDriver::Error::SerializationError => e
  raise unless e.message =~ /required but was missing/
  WebDriver.logger.warn("tolerated: #{e.message}")
end

When it happens

Trigger: A BiDi response omits a field the schema marks required. Only raises when SE_BIDI_STRICT is enabled; otherwise logs a :bidi_missing_required warning and returns UNSET.

Common situations: Running tests/binary with SE_BIDI_STRICT=1, older browser that does not yet emit the field, newer Selenium schema adding a required field the browser has not shipped, grid stripping fields.

Related errors

• #{name} expected an object on the wire, got #{json_payload.i
• #{name}##{field.name} received null but is not nullable
• #{name}##{field.name} expected #{field.list ? 'a list' : 'a
• #{name}##{field.name} expected #{field.primitive}, got #{raw
• #{name}##{field.name} expected a [key, value] pair, got #{el

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/e01a32ad03a39d52. Report an issue: GitHub.