How to access the date_modified property correctly?

[drh-stanford]

Descriptive summary

We're using v1.5.0 and have a question about the date_modified property. It's defined as a single valued property with the DC.modified predicate and indexed as a :date, but we're always getting nil from using the date_modified method in the SolrDocumentBehavior.

Expected behavior

date_modified should use the SolrDocument field date_modified_dtsi.

Actual behavior

date_modified use the SolrDocument field date_modified_ssi.

  #<SolrDocument:0x007fdb61d6f508
   @_source=
    {"system_create_dtsi"=>"2016-09-01T19:48:42Z",
     "system_modified_dtsi"=>"2016-09-01T19:48:42Z",
     "has_model_ssim"=>["VectorWork"],
     "id"=>"geo-work-1",
     "accessControl_ssim"=>["76d015f5-8f53-486a-a9f0-e84ed276d3b3"],
     "depositor_ssim"=>["[email protected]"],
     "depositor_tesim"=>["[email protected]"],
     "title_tesim"=>["Geo Work"],
     "title_sim"=>["Geo Work"],
     "date_modified_ssi"=>"2016-09-01T19:48:41Z",

See https://github.com/projecthydra/curation_concerns/blob/master/app/models/concerns/curation_concerns/required_metadata.rb#L24 for where the property is defined.

See https://github.com/projecthydra/curation_concerns/blob/master/app/presenters/curation_concerns/work_show_presenter.rb#L39 for where the presenter delegates to the SolrDocument.

See https://github.com/projecthydra/curation_concerns/blob/master/app/models/concerns/curation_concerns/solr_document_behavior.rb#L77 for where the SolrDocument gets the date_modified method.

Steps to reproduce the behavior

1. Create a work in the UI
2. Open a debugger and print out the SolrDocument associated with the presenter

Related work

N/A

cc @eliotjordan