No need to check nil

```ruby
nil.respond_to?(:stringify_keys) # => false
```

```ruby
include ActiveModel::AttributeAssignment
Object.new.assign_attributes(nil) #  => ArgumentError: When assigning attributes, you must pass a hash as an argument.
```

1 files changed, 1 insertions, 1 deletions

diff --git a/activemodel/lib/active_model/attribute_assignment.rb b/activemodel/lib/active_model/attribute_assignment.rb
index 7dad3b6dff..ee130df989 100644
--- a/activemodel/lib/active_model/attribute_assignment.rb
+++ b/activemodel/lib/active_model/attribute_assignment.rb
@@ -27,7 +27,7 @@ module ActiveModel
       if !new_attributes.respond_to?(:stringify_keys)
         raise ArgumentError, "When assigning attributes, you must pass a hash as an argument."
       end
-      return if new_attributes.nil? || new_attributes.empty?
+      return if new_attributes.empty?
 
       attributes = new_attributes.stringify_keys
       _assign_attributes(sanitize_for_mass_assignment(attributes))