Fix case where a variable name is falsy

lib/liquid/variable.rb

@@ -83,7 +83,7 @@ module Liquid
     end
 
     def render(context)
-      return ''.freeze unless @name
+      return ''.freeze if @name.nil?
       @filters.inject(context.evaluate(@name)) do |output, (filter_name, filter_args, filter_kwargs)|
         filter_args = evaluate_filter_expressions(context, filter_args, filter_kwargs)
         output = context.invoke(filter_name, output, *filter_args)

test/integration/tags/if_else_tag_test.rb

@@ -8,6 +8,7 @@ class IfElseTagTest < Minitest::Test
     assert_template_result('  this text should go into the output  ',
                            ' {% if true %} this text should go into the output {% endif %} ')
     assert_template_result('  you rock ?','{% if false %} you suck {% endif %} {% if true %} you rock {% endif %}?')
+    assert_template_result(' NO ','{% assign v = false %}{% if v %} YES {% else %} NO {% endif %}')
   end
 
   def test_if_else

test/integration/variable_test.rb

@@ -31,6 +31,7 @@ class VariableTest < Minitest::Test
 
   def test_false_renders_as_false
     assert_equal 'false', Template.parse("{{ foo }}").render!('foo' => false)
+    assert_equal 'false', Template.parse("{{ false }}").render!
   end
 
   def test_preset_assigns