```ruby
Mime::Type.register "application/x-mpac", :mpac

# Let's action_dispatch parse the params into the params hash when it receives an mpac request.
# No idea how to get this in there without adding it to this DEFAULT_PARSERS hash.
ActionDispatch::Request.parameter_parsers.merge!(Mime::MPAC =>
  lambda do |contents|
    data = MessagePack.unpack(contents)
    data.with_indifferent_access
  end
)
```

Fix deprecation warning: DEPRECATION WARNING: Accessing mime types via constants is deprecated. Please change `Mime::MPAC` to `Mime[:mpac]`
user
```ruby
Mime::Type.register "application/x-mpac", :mpac

# Let's action_dispatch parse the params into the params hash when it receives an mpac request.
# No idea how to get this in there without adding it to this DEFAULT_PARSERS hash.
ActionDispatch::Request.parameter_parsers.merge!(Mime[:mpac] =>
  lambda do |contents|
    data = MessagePack.unpack(contents)
    data.with_indifferent_access
  end
)
```
assistant