Default config should be valid, but no-op.

When a user passes the pipeline configuration via ENV (see #30), that config is merged with the default config resulting in unexpected behaviour. The default config should do nothing, successfully.

Start by tracing how pipeline configuration supplied through ENV is merged with the default configuration. Verify the resulting behavior when the default configuration is used alone and when ENV configuration is present. Done means the default configuration is valid, performs no actions, and does not introduce unexpected behavior during the merge.

Written by the indexing model from the issue text.