Refactor matcher compiler on ignore expressions

lib/mutant/matcher/compiler.rb

@@ -40,15 +40,11 @@ module Mutant
       #
       # @api private
       def ignored_subjects
-        rejectors = config.ignore_expressions.map(&SubjectPrefix.method(:new))
-
-        if rejectors.any?
-          Morpher::Evaluator::Predicate::Boolean::Negation.new(
-            Morpher::Evaluator::Predicate::Boolean::Or.new(rejectors)
+        Morpher::Evaluator::Predicate::Boolean::Negation.new(
+          Morpher::Evaluator::Predicate::Boolean::Or.new(
+            config.ignore_expressions.map(&SubjectPrefix.method(:new))
           )
-        else
-          Morpher::Evaluator::Predicate::Tautology.new
-        end
+        )
       end
 
       # Matcher for expression on env

spec/unit/mutant/matcher/compiler_spec.rb

@@ -14,7 +14,7 @@ RSpec.describe Mutant::Matcher::Compiler do
   end
 
   let(:expected_predicate) do
-    Morpher.compile(s(:true))
+    Morpher.compile(s(:negate, s(:or)))
   end
 
   describe '.call' do
@@ -41,7 +41,7 @@ RSpec.describe Mutant::Matcher::Compiler do
         it { should eql(expected_matcher) }
       end
 
-      context 'and a subject ignore' do
+      context 'and ignore epxressions' do
         let(:attributes) do
           {
             match_expressions:  [expression_a],