diff --git a/lib/cancan/ability.rb b/lib/cancan/ability.rb
index 11e9b4b..07fe5a4 100644
--- a/lib/cancan/ability.rb
+++ b/lib/cancan/ability.rb
@@ -202,10 +202,7 @@ module CanCan
     def conditions(action, subject, options = {})
       matched = matching_can_definition(action, subject)
       unless matched.empty?
-        if matched.any?{|can_definition| 
-		cond = can_definition.conditions
-		(cond.nil? || cond.empty?) && can_definition.block 
-		}
+        if matched.any?{|can_definition| can_definition.conditions_empty? && can_definition.block }
           raise Error, "Cannot determine ability conditions from block for #{action.inspect} #{subject.inspect}"
         end
         matched.map{|can_definition|
@@ -239,20 +236,19 @@ module CanCan
       false_cond = subject.send(:sanitize_sql, ['?=?', true, false])
       conds.reverse.inject(nil) do |sql, action|
         behavior, condition = action
-        if condition && !condition.empty?
+        if condition && condition != {}
           condition = "#{subject.send(:sanitize_sql, condition)}"
-          condition = "not (#{condition})" if behavior == false
+          case sql
+            when nil then condition
+            when true_cond
+              behavior ? true_cond : "not (#{condition})"
+            when false_cond
+              behavior ? condition : false_cond
+            else
+              behavior ? "(#{condition}) OR (#{sql})" : "not (#{condition}) AND (#{sql})"
+          end
         else
-          condition = behavior ? true_cond : false_cond
-        end
-        case sql
-          when nil then condition
-          when true_cond
-            behavior ? true_cond : condition
-          when false_cond
-            behavior ? condition : false_cond
-          else
-            behavior ? "(#{condition}) OR (#{sql})" : "#{condition} AND (#{sql})"
+          behavior ? true_cond : false_cond
         end
       end
     end
@@ -262,7 +258,7 @@ module CanCan
     def association_joins(action, subject)
       can_definitions = matching_can_definition(action, subject)
       unless can_definitions.empty?
-        if can_definitions.any?{|can_definition| can_definition.conditions.nil? && can_definition.block }
+        if can_definitions.any?{|can_definition| can_definition.conditions_empty? && can_definition.block }
           raise Error, "Cannot determine association joins from block for #{action.inspect} #{subject.inspect}"
         end
         collect_association_joins(can_definitions)
@@ -283,7 +279,7 @@ module CanCan
           can_definition.expand_actions(aliased_actions)
           if can_definition.matches? action, subject
             yield can_definition
-            break if can_definition.conditions.nil? && can_definition.block.nil?
+            break if can_definition.definitive?
           end
         end
       else
diff --git a/lib/cancan/can_definition.rb b/lib/cancan/can_definition.rb
index e044ac8..f4a2116 100644
--- a/lib/cancan/can_definition.rb
+++ b/lib/cancan/can_definition.rb
@@ -51,7 +51,16 @@ module CanCan
       end
     end
 
+    def definitive?
+      conditions_empty? && @block.nil?
+    end
+
+    def conditions_empty?
+      @conditions == {} || @conditions.nil?
+    end
+
     def association_joins(conditions = @conditions)
+      return nil unless conditions.kind_of?(Hash)
       joins = []
       conditions.each do |name, value|
         if value.kind_of? Hash
@@ -81,8 +90,6 @@ module CanCan
         call_block(action, subject, extra_args)
       elsif @conditions.kind_of?(Hash) && subject.class != Class
         matches_conditions?(subject)
-      elsif [true, false, :_NOT_MATCHES].include? @conditions
-        @conditions
       else
         true
       end