diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index b60afd1560e..57286f255f4 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -193,9 +193,7 @@ class IssuableBaseService < BaseService
       todo_service.mark_todo(issuable, current_user)
     when 'done'
       todo = TodosFinder.new(current_user).execute.find_by(target: issuable)
-      if todo
-        todo_service.mark_todos_as_done([todo], current_user)
-      end
+      todo_service.mark_todos_as_done([todo], current_user) if todo
     end
   end
 
diff --git a/app/services/slash_commands/interpret_service.rb b/app/services/slash_commands/interpret_service.rb
index cb0dca94036..dc4a892b8b1 100644
--- a/app/services/slash_commands/interpret_service.rb
+++ b/app/services/slash_commands/interpret_service.rb
@@ -18,11 +18,11 @@ module SlashCommands
 
       content, commands = extractor.extract_commands(content, opts)
 
-      commands.each do |name, *args|
+      commands.each do |name, args|
         definition = self.class.command_definitions_by_name[name.to_sym]
         next unless definition
 
-        definition.execute(self, opts, *args)
+        definition.execute(self, opts, args)
       end
 
       [content, @updates]
@@ -76,7 +76,6 @@ module SlashCommands
     command :assign do |assignee_param|
       user = extract_references(assignee_param, :user).first
       user ||= User.find_by(username: assignee_param)
-      user ||= User.find_by(name: assignee_param)
 
       @updates[:assignee_id] = user.id if user
     end
diff --git a/lib/gitlab/slash_commands/command_definition.rb b/lib/gitlab/slash_commands/command_definition.rb
index 641c92e77da..2ff8f4eddf0 100644
--- a/lib/gitlab/slash_commands/command_definition.rb
+++ b/lib/gitlab/slash_commands/command_definition.rb
@@ -6,11 +6,11 @@ module Gitlab
       def initialize(name, attributes = {})
         @name = name
 
-        @aliases          =  attributes[:aliases] || []
-        @description      =  attributes[:description] || ''
-        @params           =  attributes[:params] || []
-        @condition_block  =  attributes[:condition_block]
-        @action_block     =  attributes[:action_block]
+        @aliases         = attributes[:aliases] || []
+        @description     = attributes[:description] || ''
+        @params          = attributes[:params] || []
+        @condition_block = attributes[:condition_block]
+        @action_block    = attributes[:action_block]
       end
 
       def all_names
@@ -28,13 +28,13 @@ module Gitlab
         context.instance_exec(&condition_block)
       end
 
-      def execute(context, opts, *args)
+      def execute(context, opts, args)
         return if noop? || !available?(opts)
 
         block_arity = action_block.arity
-        return unless block_arity == -1 || block_arity == args.size
+        return unless (args.present? && block_arity == 1) || (args.blank? && block_arity <= 0)
 
-        context.instance_exec(*args, &action_block)
+        context.instance_exec(args, &action_block)
       end
 
       def to_h(opts)
diff --git a/lib/gitlab/slash_commands/extractor.rb b/lib/gitlab/slash_commands/extractor.rb
index 02c4c8c492e..c790b825347 100644
--- a/lib/gitlab/slash_commands/extractor.rb
+++ b/lib/gitlab/slash_commands/extractor.rb
@@ -50,15 +50,6 @@ module Gitlab
       end
 
       private
-
-      def command_names(opts)
-        command_definitions.flat_map do |command|
-          next if command.noop?
-
-          command.all_names
-        end.compact
-      end
-
       # Builds a regular expression to match known commands.
       # First match group captures the command name and
       # second match group captures its arguments.
@@ -117,6 +108,14 @@ module Gitlab
             )
         }mx
       end
+
+      def command_names(opts)
+        command_definitions.flat_map do |command|
+          next if command.noop?
+
+          command.all_names
+        end.compact
+      end
     end
   end
 end