Pipeline using explode and concat fails

Problem/Motivation

While working on #2620364: Variable to config: theme settings [d7] I discovered that the get plugin fails when a previous plugin returns multiple true.

The part of the process pipeline with the problem is the conversion of the D7 theme setting name to the D8 configuration name. Seemed simple enough but it doesn't work.

process:
  # build the configuration name from the variable name, i.e.
  # theme_bartik_settings becomes bartik.settings
  configuration_name:
    -
      plugin: explode
      source: name
      delimiter: _
    -
      plugin: extract
      index:
        - 1
    -
      plugin: concat
      source:
        -
        - constants/config_suffix

This pipeline works if both extract and get use 'handle_multiples = TRUE'. Note that #2500495: Upgrade path for Color 7.x uses this same pattern.

Data model changes

Proposed resolution

Add 'handles_multiples = TRUE' to the Get annotation.

Remaining tasks

User interface changes

N/A

API changes