Update String#camelize to provide feedback when wrong option is passed

String#camelize was returning nil without any feedback when an
invalid option was passed as parameter. This update makes the method
to raises an ArgumentError when the option passed is invalid, similar
to what Ruby does for String#downcase (and others) in 2.4.1.

https://ruby-doc.org/core-2.4.1/String.html#method-i-downcase

3 files changed, 27 insertions, 0 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 938d4f9d31..e3a39cb8c9 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,21 @@
+*   Update String#camelize to provide feedback when wrong option is passed
+
+    String#camelize was returning nil without any feedback when an
+    invalid option was passed as parameter.
+
+    Previously:
+
+        'one_two'.camelize(true)
+        => nil
+
+    Now:
+
+        'one_two'.camelize(true)
+        => ArgumentError: Invalid option, use either :upper or :lower.
+
+    *Ricardo Díaz*
+
+
 *   Fix modulo operations involving durations
 
     Rails 5.1 introduce an `ActiveSupport::Duration::Scalar` class as a wrapper
diff --git a/activesupport/lib/active_support/core_ext/string/inflections.rb b/activesupport/lib/active_support/core_ext/string/inflections.rb
index 846600c623..b5bb385033 100644
--- a/activesupport/lib/active_support/core_ext/string/inflections.rb
+++ b/activesupport/lib/active_support/core_ext/string/inflections.rb
@@ -94,6 +94,8 @@ class String
       ActiveSupport::Inflector.camelize(self, true)
     when :lower
       ActiveSupport::Inflector.camelize(self, false)
+    else
+      raise ArgumentError, "Invalid option, use either :upper or :lower."
     end
   end
   alias_method :camelcase, :camelize
diff --git a/activesupport/test/core_ext/string_ext_test.rb b/activesupport/test/core_ext/string_ext_test.rb
index 0afff5aa50..9fd6d8ac0f 100644
--- a/activesupport/test/core_ext/string_ext_test.rb
+++ b/activesupport/test/core_ext/string_ext_test.rb
@@ -108,6 +108,13 @@ class StringInflectionsTest < ActiveSupport::TestCase
     assert_equal("capital", "Capital".camelize(:lower))
   end
 
+  def test_camelize_invalid_option
+    e = assert_raise ArgumentError do
+      "Capital".camelize(nil)
+    end
+    assert_equal("Invalid option, use either :upper or :lower.", e.message)
+  end
+
   def test_dasherize
     UnderscoresToDashes.each do |underscored, dasherized|
       assert_equal(dasherized, underscored.dasherize)