diff --git a/manifests/init.pp b/manifests/init.pp
index 0c97e4a..2a9a7d9 100644
--- a/manifests/init.pp
+++ b/manifests/init.pp
@@ -48,11 +48,11 @@
 class java(
   String $distribution                                              = 'jdk',
   Pattern[/present|installed|latest|^[.+_0-9a-zA-Z:~-]+$/] $version = 'present',
-  $package                                                          = undef,
+  Optional[String] $package                                         = undef,
   Optional[Array] $package_options                                  = undef,
-  $java_alternative                                                 = undef,
-  $java_alternative_path                                            = undef,
-  $java_home                                                        = undef
+  Optional[String] $java_alternative                                = undef,
+  Optional[String] $java_alternative_path                           = undef,
+  Optional[String] $java_home                                       = undef
 ) {
   include java::params