Extract a NullDisplayField that includes the necessary default values…

app/presenters/blacklight/index_presenter.rb

@@ -41,7 +41,7 @@ def fields
     end
 
     def field_config(field)
-      configuration.index_fields.fetch(field) { Configuration::NullField.new(field) }
+      configuration.index_fields.fetch(field) { Configuration::NullDisplayField.new(field) }
     end
   end
 end

app/presenters/blacklight/show_presenter.rb

@@ -9,7 +9,7 @@ def fields
     end
 
     def field_config(field)
-      configuration.show_fields.fetch(field) { Configuration::NullField.new(field) }
+      configuration.show_fields.fetch(field) { Configuration::NullDisplayField.new(field) }
     end
 
     def field_presenter_options

lib/blacklight/configuration.rb

@@ -12,6 +12,7 @@ class Configuration < OpenStructWithHashAccess
       autoload :Fields
       autoload :Field
       autoload :NullField
+      autoload :NullDisplayField
       autoload :SearchField
       autoload :FacetField
       autoload :SortField

lib/blacklight/configuration/null_display_field.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module Blacklight
+  # Returned if no config is defined for a display field in the Blacklight::Configuration
+  class Configuration::NullDisplayField < Blacklight::Configuration::DisplayField
+    def initialize(field_or_hash = nil)
+      case field_or_hash
+      when String, Symbol
+        super(field: field_or_hash)
+      else
+        super
+      end
+
+      normalize!
+    end
+  end
+end