In https://gitlab.com/gitlab-org/release/framework/issues/28 we found
that this method was changed a lot over the years: 43 times if our
calculations were correct. Looking at the method, it had quite a few
branches going on:

    def create_or_update_import_data(data: nil, credentials: nil)
      return if data.nil? && credentials.nil?

      project_import_data = import_data || build_import_data

      if data
        project_import_data.data ||= {}
        project_import_data.data = project_import_data.data.merge(data)
      end

      if credentials
        project_import_data.credentials ||= {}
        project_import_data.credentials =
          project_import_data.credentials.merge(credentials)
      end

      project_import_data
    end

If we turn the || and ||= operators into regular if statements, we can
see a bit more clearly that this method has quite a lot of branches in
it:

    def create_or_update_import_data(data: nil, credentials: nil)
      if data.nil? && credentials.nil?
        return
      else
        project_import_data =
          if import_data
            import_data
          else
            build_import_data
          end

        if data
          if project_import_data.data
            # nothing
          else
            project_import_data.data = {}
          end

          project_import_data.data =
            project_import_data.data.merge(data)
        end

        if credentials
          if project_import_data.credentials
            # nothing
          else
            project_import_data.credentials = {}
          end

          project_import_data.credentials =
            project_import_data.credentials.merge(credentials)
        end

        project_import_data
      end
    end

The number of if statements and branches here makes it easy to make
mistakes. To resolve this, we refactor this code in such a way that we
can get rid of all but the first `if data.nil? && credentials.nil?`
statement. We can do this by simply sending `to_h` to `nil` in the right
places, which removes the need for statements such as `if data`.

Since this data gets written to a database, in ProjectImportData we do
make sure to not write empty Hash values. This requires an `unless`
(which is really a `if !`), but the resulting code is still very easy to
read.