diff --git a/lamian.gemspec b/lamian.gemspec
index 3ae69dc..27d6d80 100644
--- a/lamian.gemspec
+++ b/lamian.gemspec
@@ -24,7 +24,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'bundler', '~> 1.12'
   spec.add_development_dependency 'rake', '~> 10.0'
   spec.add_development_dependency 'rspec', '~> 3.0'
-  spec.add_development_dependency 'rubocop', '~> 0.41'
+  spec.add_development_dependency 'rubocop', '~> 0.45'
   spec.add_development_dependency 'pry', '~> 0.10'
   spec.add_development_dependency 'coveralls', '~> 0.8'
 end
diff --git a/lib/lamian/logger.rb b/lib/lamian/logger.rb
index 99093f8..f2908cd 100644
--- a/lib/lamian/logger.rb
+++ b/lib/lamian/logger.rb
@@ -26,17 +26,19 @@ def add(*args, &block)
     end
 
     def dump(format: nil)
-      result = logdevs[-1].string.dup
-      format ? apply_format(format, result) : result
+      result = logdevs[-1]&.string&.dup
+      apply_format!(format, result)
+      result
     end
 
     private
 
     attr_accessor :level, :logdevs, :formatter
 
-    def apply_format(_format, result)
+    def apply_format!(format, result)
+      return unless format
+      return unless result
       result.gsub!(/\[\d{1,2}m/, '')
-      result
     end
 
     def push_logdev(logdev)
diff --git a/lib/lamian/version.rb b/lib/lamian/version.rb
index 54b56b2..5195219 100644
--- a/lib/lamian/version.rb
+++ b/lib/lamian/version.rb
@@ -1,4 +1,4 @@
 # frozen_string_literal: true
 module Lamian
-  VERSION = '0.3.2'
+  VERSION = '0.3.3'
 end
diff --git a/spec/lamian/logger_spec.rb b/spec/lamian/logger_spec.rb
index 514bb1b..b162613 100644
--- a/spec/lamian/logger_spec.rb
+++ b/spec/lamian/logger_spec.rb
@@ -1,9 +1,18 @@
 # frozen_string_literal: true
-describe Lamian::Logger, :cool_loggers do
-  specify '#run' do
-    Lamian.run do
+describe Lamian::Logger do
+  describe '#dump', :cool_loggers do
+    specify 'with #run' do
+      Lamian.run do
+        generic_logger.info "it's alive"
+        expect(Lamian.dump).to eq "it's alive\n"
+        expect(Lamian.dump).to eq "it's alive\n"
+      end
+    end
+
+    specify 'without #run' do
       generic_logger.info "it's alive"
-      expect(Lamian.dump).to eq "it's alive\n"
+      expect { Lamian.dump }.not_to raise_error
+      expect(Lamian.dump).to be_nil
     end
   end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 4c1b569..b8bdfa7 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -13,7 +13,7 @@
   let(:generic_logger) { Logger.new(generic_logger_buffer) }
 
   let(:cool_formatter) do
-    -> (_severity, _date, _progname, message) { "#{message}\n" }
+    ->(_severity, _date, _progname, message) { "#{message}\n" }
   end
 
   before('extend generic_logger') { Lamian.extend_logger(generic_logger) }