Do not show suggestion message when not exist suggestion

**before**

```
$ ./bin/rails g g
Could not find generator 'g'. Maybe you meant nil?
Run `rails generate --help` for more options.
```

**after**

```
$ ./bin/rails g g
Could not find generator 'g'.
Run `rails generate --help` for more options.
```

railties/lib/rails/commands/server/server_command.rb

@@ -302,9 +302,10 @@ module Rails
             MSG
           else
             suggestion = Rails::Command::Spellchecker.suggest(server, from: RACK_SERVERS)
+            suggestion_msg = "Maybe you meant #{suggestion.inspect}?" if suggestion
 
             <<~MSG
-              Could not find server "#{server}". Maybe you meant #{suggestion.inspect}?
+              Could not find server "#{server}". #{suggestion_msg}
               Run `rails server --help` for more options.
             MSG
           end

railties/lib/rails/generators.rb

@@ -272,8 +272,10 @@ module Rails
         else
           options     = sorted_groups.flat_map(&:last)
           suggestion  = Rails::Command::Spellchecker.suggest(namespace.to_s, from: options)
+          suggestion_msg = "Maybe you meant #{suggestion.inspect}?" if suggestion
+
           puts <<~MSG
-            Could not find generator '#{namespace}'. Maybe you meant #{suggestion.inspect}?
+            Could not find generator '#{namespace}'. #{suggestion_msg}
             Run `rails generate --help` for more options.
           MSG
         end

railties/test/commands/server_test.rb

@@ -32,6 +32,12 @@ class Rails::Command::ServerCommandTest < ActiveSupport::TestCase
     assert_match(/Could not find server "tin". Maybe you meant "thin"?/, run_command("--using", "tin"))
   end
 
+  def test_using_server_mistype_without_suggestion
+    output = run_command("--using", "t")
+    assert_match(/Could not find server "t"/, output)
+    assert_no_match(/Maybe you meant/, output)
+  end
+
   def test_using_positional_argument_deprecation
     assert_match(/DEPRECATION WARNING/, run_command("tin"))
   end

railties/test/generators_test.rb

@@ -28,6 +28,7 @@ class GeneratorsTest < Rails::Generators::TestCase
     output = capture(:stdout) { Rails::Generators.invoke name }
     assert_match "Could not find generator '#{name}'", output
     assert_match "`rails generate --help`", output
+    assert_no_match "Maybe you meant", output
   end
 
   def test_generator_suggestions