Fix in [] to be false, in [] to be true

This is in response to discussion on 62207fa

Author: ernie

lib/arel/visitors/to_sql.rb

@@ -370,11 +370,19 @@ def visit_Arel_Table o
       end
 
       def visit_Arel_Nodes_In o
-        "#{visit o.left} IN (#{visit o.right})"
+        if Array === o.right && o.right.empty?
+          '1=0'
+        else
+          "#{visit o.left} IN (#{visit o.right})"
+        end
       end
 
       def visit_Arel_Nodes_NotIn o
-        "#{visit o.left} NOT IN (#{visit o.right})"
+        if Array === o.right && o.right.empty?
+          '1=1'
+        else
+          "#{visit o.left} NOT IN (#{visit o.right})"
+        end
       end
 
       def visit_Arel_Nodes_And o

test/visitors/test_to_sql.rb

@@ -167,11 +167,9 @@ def dispatch
           }
         end
 
-        it "should return IN () when empty right which is invalid SQL" do
+        it "should return 1=0 when empty right which is always false" do
           node = @attr.in []
-          @visitor.accept(node).must_be_like %{
-            "users"."id" IN ()
-          }
+          @visitor.accept(node).must_equal '1=0'
         end
 
         it 'can handle two dot ranges' do
@@ -255,11 +253,9 @@ def quote value, column = nil
           }
         end
 
-        it "should return NOT IN () when empty right which is invalid SQL" do
+        it "should return 1=1 when empty right which is always true" do
           node = @attr.not_in []
-          @visitor.accept(node).must_be_like %{
-            "users"."id" NOT IN ()
-          }
+          @visitor.accept(node).must_equal '1=1'
         end
 
         it 'can handle two dot ranges' do