Don't call backup unless the FileType supports it

Some FileTypes, such as those that deal with crontabs, don't implement the
`backup` method.

lib/puppetx/filemapper.rb

@@ -296,7 +296,7 @@ def perform_write(filename, contents)
       @mapped_files[filename][:filetype] ||= Puppet::Util::FileType.filetype(self.filetype).new(filename)
       filetype = @mapped_files[filename][:filetype]
 
-      filetype.backup
+      filetype.backup if filetype.respond_to? :backup
       filetype.write(contents)
     end
 
@@ -308,7 +308,7 @@ def remove_empty_file(filename)
         @mapped_files[filename][:filetype] ||= Puppet::Util::FileType.filetype(self.filetype).new(filename)
         filetype = @mapped_files[filename][:filetype]
 
-        filetype.backup
+        filetype.backup if filetype.respond_to? :backup
 
         File.unlink(filename)
       end

spec/unit/puppetx/filemapper_spec.rb

@@ -505,6 +505,33 @@ def select_file; '/single/file/provider'; end
       subject.load_all_providers_from_disk
     end
 
+    describe 'that does not implement backup' do
+      let(:resource) { resource = dummytype.new(params_yay) }
+      let(:stub_filetype) { stub() }
+
+      before :each do
+        subject.mapped_files['/multiple/file/provider-flush'][:filetype] = stub_filetype
+        subject.dirty_file!('/multiple/file/provider-flush')
+
+        stub_filetype.expects(:respond_to?).with(:backup).returns(false)
+        stub_filetype.expects(:backup).never
+      end
+
+      it 'should not call backup when writing files' do
+        stub_filetype.stubs(:write)
+
+        resource.flush
+      end
+
+      it 'should not call backup when unlinking files' do
+        subject.unlink_empty_files = true
+        subject.stubs(:format_file).returns ''
+        File.stubs(:exist?).with('/multiple/file/provider-flush').returns true
+        File.stubs(:unlink)
+
+        resource.flush
+      end
+    end
   end
 
   describe 'flush hooks' do