Blacklist Blacklight::Document#empty? to avoid ActiveModel deprecatio…

…n on validation

app/models/concerns/blacklight/document.rb

@@ -37,7 +37,7 @@ module Blacklight::Document
     extend ActiveModel::Naming
     include Blacklight::Document::Extensions
     include GlobalID::Identification
-  end    
+  end
 
   attr_reader :response, :_source
   alias_method :solr_response, :response
@@ -69,15 +69,14 @@ def method_missing(m, *args, &b)
   end
 
   def respond_to_missing? m, *args
-    return super if m == :to_hash
-
+    return super if %i(empty? to_hash).include?(m)
     _source_responds_to?(m, *args) || super
   end
 
   # Helper method to check if value/multi-values exist for a given key.
   # The value can be a string, or a RegExp
   # Multiple "values" can be given; only one needs to match.
-  # 
+  #
   # Example:
   # doc.has?(:location_facet)
   # doc.has?(:location_facet, 'Clemons')
@@ -141,12 +140,12 @@ def more_like_this
   module ClassMethods
     attr_writer :unique_key
     def unique_key
-      @unique_key ||= 'id' 
+      @unique_key ||= 'id'
     end
   end
-  
+
   private
-  
+
   def _source_responds_to? *args
     _source && self != _source && _source.respond_to?(*args)
   end