Do not compact before checking minItems

Fixes voxpupuli#129

lib/json-schema/attributes/minitems.rb

@@ -4,7 +4,7 @@ module JSON
   class Schema
     class MinItemsAttribute < Attribute
       def self.validate(current_schema, data, fragments, processor, validator, options = {})
-        if data.is_a?(Array) && (data.compact.size < current_schema.schema['minItems'])
+        if data.is_a?(Array) && (data.size < current_schema.schema['minItems'])
           message = "The property '#{build_fragment(fragments)}' did not contain a minimum number of items #{current_schema.schema['minItems']}"
           validation_error(processor, message, fragments, current_schema, self, options[:record_errors])
         end

test/test_minitems.rb

@@ -0,0 +1,18 @@
+require 'test/unit'
+require File.dirname(__FILE__) + '/../lib/json-schema'
+
+class MinItemsTest < Test::Unit::TestCase
+  def test_minitems_nils
+    schema = {
+      "type" => "array",
+      "minItems" => 1,
+      "items" => { "type" => "object" }
+    }
+    data = [nil]
+
+    errors = JSON::Validator.fully_validate(schema, [nil])
+    assert_equal(errors.length, 1)
+    assert(errors[0] !~ /minimum/)
+    assert(errors[0] =~ /NilClass/)
+  end
+end