Time_Key is dropped even when not parsed successfully in json parser

[braydonk]

Bug Report

Describe the bug
In the parser configuration docs: https://github.com/fluent/fluent-bit-docs/blob/4f06d31577aa476cf888d2829f94d84e6d1c323d/pipeline/parsers/configuring-parser.md#configuration-parameters

The Time_Keep field documentation says the following:

By default when a time key is recognized and parsed, the parser will drop the original time field.

This implies to me that if the time value fails to parse, the key should not be dropped. This is not the case with the json parser. If a time value fails to parse, the Time_Key is dropped regardless.

To Reproduce

• Example log message if applicable:

{"time":"nonsense"}

• Steps to reproduce the problem:

1. Using the following parser:

[PARSER]
    Format      json
    Name        parse_json
    Time_Format %m-%dT%H:%M:%S.%L%Z
    Time_Key    time

Configured on a pipeline however you'd like, it's not really important. As long as it reads the example log line above and has a valid output you'll be able to see the result.

Expected behavior
time should still be present because it will fail to parse with the given Time_Format.

Your Environment

• Version used: Fluent Bit 2.0.12 and master branch

Additional context
It is possible that this is intended behaviour and that the docs are simply misleading and need an update, however I think it makes sense that the Time_Key would be kept if parsing fails.