Fix edge cases in begin mutator

lib/mutant/mutator/node/begin.rb

@@ -1,6 +1,7 @@
 module Mutant
   class Mutator
     class Node
+
       # Mutator for begin nodes
       class Begin < self
 
@@ -15,7 +16,15 @@ module Mutant
         # @api private
         #
         def dispatch
-          emit_children_mutations
+          Util::Array.each(children) do |children|
+            if children.length > 1
+              emit_self(*children)
+            end
+          end
+          children.each do |child|
+            emit(child)
+          end
+          emit(nil)
         end
 
       end # Block

spec/unit/mutant/mutator/node/begin/mutation_spec.rb

@@ -1,37 +1,33 @@
 require 'spec_helper'
 
-describe Mutant::Mutator, 'block' do
+describe Mutant::Mutator, 'begin' do
 
-  context 'with more than one statement' do
-    let(:source) { "true\nfalse" }
-
-    let(:mutations) do
-      mutations = []
-
-      # Mutation of each statement in block
-      mutations << "true\ntrue"
-      mutations << "false\nfalse"
-      mutations << "nil\nfalse"
-      mutations << "true\nnil"
-
-      # Remove statement in block
-      mutations << s(:begin, s(:true))
-      mutations << s(:begin, s(:false))
-      mutations << 'nil'
-    end
-
-    it_should_behave_like 'a mutator'
+  # This mutation and only this mutation can result in
+  # and empty emit that is parsed into nil, unparser cannot
+  # handle this so we guard this here!
+  def generate(node)
+    return '' if node.nil?
+    super
   end
 
-  context 'with one statement' do
-    let(:source) { 'true' }
+  let(:source) { "true\nfalse" }
 
-    let(:mutations) do
-      mutations = []
-      mutations << s(:false)
-      mutations << s(:nil)
-    end
+  let(:mutations) do
+    mutations = []
 
-    it_should_behave_like 'a mutator'
+    # Mutation of each statement in block
+    mutations << "true\ntrue"
+    mutations << "false\nfalse"
+    mutations << "nil\nfalse"
+    mutations << "true\nnil"
+
+    # Remove statement in block
+    mutations << 'true'
+    mutations << 'false'
+
+    # Replace block with empty
+    mutations << ''
   end
+
+  it_should_behave_like 'a mutator'
 end