Comparison operators should handle case where expectation is nil

* While this should be rare, this does occur in the dm-is-list specs when
  testing against the yaml/in_memory adapters.
* Possible optimization in the future might be to add #valid? methods to
  each gt/gte/lt/lte Comparison operator that returns false if the
  expected value is nil. This will cause the query to never execute, saving
  the comparison operator from being called when in an invalid state. The
  object may still need to handle invalid states when called stand-alone
  through.

lib/dm-core/query/conditions/comparison.rb

@@ -797,6 +797,7 @@ class GreaterThanComparison < AbstractComparison
         #
         # @api semipublic
         def matches?(record)
+          return false if expected.nil?
           record_value = record_value(record)
           !record_value.nil? && record_value > expected
         end
@@ -827,6 +828,7 @@ class LessThanComparison < AbstractComparison
         #
         # @api semipublic
         def matches?(record)
+          return false if expected.nil?
           record_value = record_value(record)
           !record_value.nil? && record_value < expected
         end
@@ -857,6 +859,7 @@ class GreaterThanOrEqualToComparison < AbstractComparison
         #
         # @api semipublic
         def matches?(record)
+          return false if expected.nil?
           record_value = record_value(record)
           !record_value.nil? && record_value >= expected
         end
@@ -885,6 +888,7 @@ class LessThanOrEqualToComparison < AbstractComparison
         #
         # @api semipublic
         def matches?(record)
+          return false if expected.nil?
           record_value = record_value(record)
           !record_value.nil? && record_value <= expected
         end

spec/semipublic/query/conditions/comparison_spec.rb

@@ -1194,6 +1194,16 @@ class Article
 
         it { should be(false) }
       end
+
+      describe 'with an expected value of nil' do
+        subject { @comparison.matches?(@model.new(@property => 2)) }
+
+        before do
+          @comparison = DataMapper::Query::Conditions::Comparison.new(@slug, @property, nil)
+        end
+
+        it { should be(false) }
+      end
     end
   end
 
@@ -1276,6 +1286,16 @@ class Article
 
         it { should be(false) }
       end
+
+      describe 'with an expected value of nil' do
+        subject { @comparison.matches?(@model.new(@property => 0)) }
+
+        before do
+          @comparison = DataMapper::Query::Conditions::Comparison.new(@slug, @property, nil)
+        end
+
+        it { should be(false) }
+      end
     end
   end
 
@@ -1358,6 +1378,16 @@ class Article
 
         it { should be(false) }
       end
+
+      describe 'with an expected value of nil' do
+        subject { @comparison.matches?(@model.new(@property => 1)) }
+
+        before do
+          @comparison = DataMapper::Query::Conditions::Comparison.new(@slug, @property, nil)
+        end
+
+        it { should be(false) }
+      end
     end
   end
 
@@ -1440,6 +1470,16 @@ class Article
 
         it { should be(false) }
       end
+
+      describe 'with an expected value of nil' do
+        subject { @comparison.matches?(@model.new(@property => 1)) }
+
+        before do
+          @comparison = DataMapper::Query::Conditions::Comparison.new(@slug, @property, nil)
+        end
+
+        it { should be(false) }
+      end
     end
   end