Classes require DateTime but do not "require 'date'"

[atz]

Error is: NameError: uninitialized constant Solrizer::FieldMapper::DateTime

Example:

2.1.2 :005 > Solrizer.default_field_mapper.solr_names_and_values("foobar", "xyz", [:searchable, :facetable, :displayable])
NameError: uninitialized constant Solrizer::FieldMapper::DateTime
    from /Users/atz/.rvm/gems/ruby-2.1.2/gems/solrizer-3.3.0/lib/solrizer/field_mapper.rb:168:in `extract_type'
    from /Users/atz/.rvm/gems/ruby-2.1.2/gems/solrizer-3.3.0/lib/solrizer/field_mapper.rb:204:in `block (2 levels) in solr_names_and_values'
    from /Users/atz/.rvm/gems/ruby-2.1.2/gems/solrizer-3.3.0/lib/solrizer/field_mapper.rb:201:in `each'
    from /Users/atz/.rvm/gems/ruby-2.1.2/gems/solrizer-3.3.0/lib/solrizer/field_mapper.rb:201:in `block in solr_names_and_values'
    from /Users/atz/.rvm/gems/ruby-2.1.2/gems/solrizer-3.3.0/lib/solrizer/field_mapper.rb:200:in `each'
    from /Users/atz/.rvm/gems/ruby-2.1.2/gems/solrizer-3.3.0/lib/solrizer/field_mapper.rb:200:in `solr_names_and_values'
    from (irb):5
    from /Users/atz/.rvm/rubies/ruby-2.1.2/bin/irb:11:in `<main>'
2.1.2 :006 > require "date"
 => true 
2.1.2 :007 > Solrizer.default_field_mapper.solr_names_and_values("foobar", "xyz", [:searchable, :facetable, :displayable])
 => {"foobar_teim"=>["xyz"], "foobar_sim"=>["xyz"], "foobar_ssm"=>["xyz"]} 

See:
https://github.com/projecthydra/solrizer/blob/master/lib/solrizer/field_mapper.rb#L168

Note: Code works as long as date is loaded (which probably conceals the bug in most environments).

A similar error could also be elicited from default_descriptors.rb. Add require 'date' to both classes (or base class?) to resolve.