diff --git a/bin/json_cli b/bin/json_cli
index 8556a6a..40571c1 100755
--- a/bin/json_cli
+++ b/bin/json_cli
@@ -3,51 +3,52 @@ require 'json_cli'
 require 'thor'
 
 module JsonCli
+  # CLI class
   class CLI < Thor
-    class_option :output, :aliases => :o, :default => '/dev/stdout'
+    class_option :output, aliases: :o, default: '/dev/stdout'
 
-    desc "left_join RIGHT_FILE [LEFT_FILE]", "left outer join of json files"
-    option :join_key, :required => true, :aliases => :k
-    def left_join(right_file, left_file = nil)
-      left_io = left_file.nil? ? STDIN : File.open(left_file, 'r')
+    desc 'left_join RIGHT_FILE [LEFT_FILE]', 'left outer join of json files'
+    option :join_key, required: true, aliases: :k
+    def left_join(right_file, left_file = '/dev/stdin')
+      left_io = File.open(left_file, 'r')
       right_io = File.open(right_file, 'r')
       JsonCli::JoinJson.left_join(left_io, right_io, opts)
       [left_io, right_io, opts[:out]].each(&:close)
     end
 
-    desc "right_join RIGHT_FILE [LEFT_FILE]", "right outer join of json files"
-    option :join_key, :required => true, :aliases => :k
-    def right_join(right_file, left_file = nil)
-      left_io = left_file.nil? ? STDIN : File.open(left_file, 'r')
+    desc 'right_join RIGHT_FILE [LEFT_FILE]', 'right outer join of json files'
+    option :join_key, required: true, aliases: :k
+    def right_join(right_file, left_file = '/dev/stdin')
+      left_io = File.open(left_file, 'r')
       right_io = File.open(right_file, 'r')
       JsonCli::JoinJson.right_join(left_io, right_io, opts)
       [left_io, right_io, opts[:out]].each(&:close)
     end
 
-    desc "inner_join RIGHT_FILE [LEFT_FILE]", "inner join of json files"
-    option :join_key, :required => true, :aliases => :k
-    def inner_join(right_file, left_file = nil)
-      left_io = left_file.nil? ? STDIN : File.open(left_file, 'r')
+    desc 'inner_join RIGHT_FILE [LEFT_FILE]', 'inner join of json files'
+    option :join_key, required: true, aliases: :k
+    def inner_join(right_file, left_file = '/dev/stdin')
+      left_io = File.open(left_file, 'r')
       right_io = File.open(right_file, 'r')
       JsonCli::JoinJson.inner_join(left_io, right_io, opts)
       [left_io, right_io, opts[:out]].each(&:close)
     end
 
-    desc "unwind_array [JSON_FILE]", "unwind array of json file"
-    option :unwind_key, :required => true, :aliases => :k
-    def unwind_array(json_file = nil)
-      io = json_file.nil? ? STDIN : File.open(json_file, 'r')
+    desc 'unwind_array [JSON_FILE]', 'unwind array of json file'
+    option :unwind_key, required: true, aliases: :k
+    def unwind_array(json_file = '/dev/stdin')
+      io = File.open(json_file, 'r')
       JsonCli::UnwindJson.unwind_array(io, opts)
       [io, opts[:out]].each(&:close)
     end
 
-    desc "unwind_hash [JSON_FILE]", "unwind hash of json file"
-    option :unwind_key, :required => true, :aliases => :k
-    option :flatten, :type => :boolean, :aliases => :f
+    desc 'unwind_hash [JSON_FILE]', 'unwind hash of json file'
+    option :unwind_key, required: true, aliases: :k
+    option :flatten, type: :boolean, aliases: :f
     option :key_label
     option :value_label
-    def unwind_hash(json_file = nil)
-      io = json_file.nil? ? STDIN : File.open(json_file, 'r')
+    def unwind_hash(json_file = '/dev/stdin')
+      io = File.open(json_file, 'r')
       JsonCli::UnwindJson.unwind_hash(io, opts)
       [io, opts[:out]].each(&:close)
     end