diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9c563a2..450bfd7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,7 +7,7 @@ jobs:
     strategy:
       matrix:
         os:   ['ubuntu', 'macos']
-        ruby: [ '2.6', '2.7', '3.0' ]
+        ruby: [ '2.4', '2.5', '2.6', '2.7', '3.0' ]
     steps:
       - uses: actions/checkout@v2
       - uses: ruby/setup-ruby@v1
diff --git a/lib/youplot/dsv.rb b/lib/youplot/dsv.rb
index b1d48fc..8dbd8f2 100644
--- a/lib/youplot/dsv.rb
+++ b/lib/youplot/dsv.rb
@@ -14,7 +14,7 @@ module YouPlot
 
       # Remove blank lines
       arr.delete_if do |i|
-        i == [] or i.all? nil
+        i == [] or i.all?(&:nil?)
       end
 
       # get header
diff --git a/lib/youplot/options.rb b/lib/youplot/options.rb
index 8c4aba0..ab169c6 100644
--- a/lib/youplot/options.rb
+++ b/lib/youplot/options.rb
@@ -13,7 +13,6 @@ module YouPlot
     :encoding,
     :reverse,      # count
     :color_names,  # color
-    :debug,
-    keyword_init: true
+    :debug
   )
 end
diff --git a/lib/youplot/parser.rb b/lib/youplot/parser.rb
index 94519b3..a9d7130 100644
--- a/lib/youplot/parser.rb
+++ b/lib/youplot/parser.rb
@@ -15,17 +15,16 @@ module YouPlot
       @command = nil
 
       @options = Options.new(
-        delimiter: "\t",
-        transpose: false,
-        headers: nil,
-        pass: false,
-        output: $stderr,
-        fmt: 'xyy',
-        progressive: false,
-        encoding: nil,
-        reverse: false,
-        color_names: false,
-        debug: false
+        "\t",    # elimiter:
+        false,   # transpose:
+        nil,     # headers:
+        false,   # pass:
+        $stderr, # output:
+        'xyy',   # fmt:
+        false,   # progressive:
+        nil,     # encoding:
+        false,   # color_names:
+        false    # debug:
       )
 
       @params = Parameters.new