Fix bug

Author: johnnyshields

lib/mongoid/fields/field_types.rb

@@ -36,11 +36,12 @@ module FieldTypes
       }.with_indifferent_access.freeze
 
       def get(value)
+        value = value.to_sym if value.is_a?(String)
         mapping[value] || handle_unmapped_type(value)
       end
 
       def define(symbol, klass)
-        mapping[symbol] = klass
+        mapping[symbol.to_sym] = klass
       end
 
       delegate :delete, to: :mapping
@@ -53,7 +54,6 @@ def handle_unmapped_type(type)
         return Object if type.nil?
 
         if type.is_a?(Module)
-          symbol = type.name.demodulize.underscore
           warn_class_type(type.name)
           return Mongoid::Boolean if type.to_s == 'Boolean'
           return type
@@ -64,6 +64,7 @@ def handle_unmapped_type(type)
 
       def warn_class_type(type)
         return if warned_class_types.include?(type)
+        symbol = type.demodulize.underscore
         Mongoid.logger.warn(
           "Using a Class (#{type}) in the field :type option is deprecated " +
           "and will be removed in a future major Mongoid version. " +