Changing to keep default_proc support

lib/liquid/context.rb

@@ -164,7 +164,7 @@ module Liquid
       # This was changed from find() to find_index() because this is a very hot
       # path and find_index() is optimized in MRI to reduce object allocation
       scope = (index = @scopes.find_index { |s| s.key?(key) }) && @scopes[index]
-      scope ||= (index = @environments.find_index { |s| s.key?(key) }) && @environments[index]
+      scope ||= (index = @environments.find_index { |s| s.key?(key) || !s.default_proc.nil? }) && @environments[index]
       scope ||= {}
 
       variable = lookup_and_evaluate(scope, key, raise_on_not_found: raise_on_not_found).to_liquid

test/integration/variable_test.rb

@@ -80,7 +80,10 @@ class VariableTest < Minitest::Test
     assigns['test'] = 'Tobi'
     assert_equal 'Hello Tobi', template.render!(assigns)
     assigns.delete('test')
-    assert_equal "Hello ", template.render!(assigns)
+    e = assert_raises(RuntimeError) do
+      template.render!(assigns)
+    end
+    assert_equal "Unknown variable 'test'", e.message
   end
 
   def test_environment_falsy