# Coming changes to config processing (Oct 2019)

**URL:** <https://discuss.circleci.com/t/coming-changes-to-config-processing-oct-2019/32862>\
**Category:** Announcements\
**Created:** [October 11, 2019, 3:57pm UTC](https://discuss.circleci.com/t/coming-changes-to-config-processing-oct-2019/32862 "2019-10-11T15:57:28Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![stig](https://sea2.discourse-cdn.com/circleci/user_avatar/discuss.circleci.com/stig/32/25107_2.png) [@stig](https://discuss.circleci.com/u/stig)\
**Post date:** [October 11, 2019, 3:57pm UTC](https://discuss.circleci.com/t/coming-changes-to-config-processing-oct-2019/32862/1 "2019-10-11T15:57:28Z")

</div>

Config processing is an area where small changes can have a large impact across our customer base. We do our best, through extensive unit, functional, and regression testing to make sure that we don’t break config processing. But sometimes we find bugs where the implementation is not conforming to specification and our regression testing tells us that there are a small number of people who will be affected by the bug fixes.

The following bugfixes will be going live next week. We have reached out to people our regression testing has shown will be affected but since we don’t test every single config some of you may encounter these stricter errors without having been contacted.

# Explicit `null` as default value is no longer accepted

We fixed a bug where a `null` default value for a parameter was accepted as a valid default. Parameters declared with a `null` default value will now always need to be passed in invocations. The following will no longer be accepted:

```yaml
jobs:
  my-job:
    machine: true
    parameters:
      foo:
        type: string
        default:
    steps:
     - ...
workflows:
  my-workflow:
    jobs:
      - my-job # this will error, the `foo` parameter must be passed

```

An error will be reported:

```auto
Error calling workflow: 'my-workflow'
Error calling job: 'my-job'
Missing required argument(s): foo"

```

# No more extra arguments to jobs/executors/commands

The compiler is stricter about passing extra arguments that don’t match formal parameters to jobs/executors/commands. Invocations like the following will no longer be accepted:

```yaml
jobs:
  my-job:
    machine: true
    steps:
      - run: echo hello
workflows:
  my-workflow:
    jobs:
      - my-job:
          unknown_arg: "hi" # this will error, unknown_arg is not a formal parameter for my-job

```

An error will be reported instead:

```auto
Error calling workflow: 'my-workflow'
Error calling job: 'my-job'
Unexpected argument(s): unknown_arg

```

The reason we disallow this is because it can hide other errors, for example where a block of YAML has been indented incorrectly.