Fix MethodLiteral for updated blank & empty

lib/liquid/binary_expression.rb

@@ -72,7 +72,7 @@ module Liquid
     end
 
     def apply_method_literal(node, other)
-      other.send(node.method_name) if other.respond_to?(node.method_name)
+      node.apply(other)
     end
 
     def equal_variables(left, right)

lib/liquid/expression.rb

@@ -9,8 +9,8 @@ module Liquid
       '' => nil,
       'true' => true,
       'false' => false,
-      'blank' => MethodLiteral.new(:blank?, '').freeze,
-      'empty' => MethodLiteral.new(:empty?, '').freeze,
+      'blank' => MethodLiteral::BLANK,
+      'empty' => MethodLiteral::EMPTY,
     }.freeze
 
     DOT = ".".ord

lib/liquid/method_literal.rb

@@ -4,13 +4,46 @@ module Liquid
   class MethodLiteral
     attr_reader :method_name, :to_s
 
-    def initialize(method_name, to_s)
+    def initialize(method_name, to_s, &evaluator)
       @method_name = method_name
       @to_s = to_s
+      @evaluator = evaluator
+    end
+
+    def apply(value)
+      if value.respond_to?(@method_name)
+        value.send(@method_name)
+      elsif @evaluator
+        @evaluator.call(value)
+      end
     end
 
     def to_liquid
       to_s
     end
+
+    BLANK = MethodLiteral.new(:blank?, '') do |value|
+      case value
+      when NilClass, FalseClass
+        true
+      when TrueClass, Numeric
+        false
+      when String
+        value.empty? || value.match?(/\A\s*\z/)
+      when Array, Hash
+        value.empty?
+      else
+        value.respond_to?(:empty?) ? value.empty? : false
+      end
+    end.freeze
+
+    EMPTY = MethodLiteral.new(:empty?, '') do |value|
+      case value
+      when String, Array, Hash
+        value.empty?
+      else
+        value.respond_to?(:empty?) ? value.empty? : nil
+      end
+    end.freeze
   end
 end