FeatureSummary: Do not force OPTIONAL type in SET_PACKAGE_PROPERTIES

The OPTIONAL type is used anyway as default when the type is not set

Since RUNTIME < OPTIONAL, forcing it here forces the user to set
"RUNTIME" at the first SET_PACKAGE_PROPERTIES, otherwise it is
impossible to set it later.
Without this it is impossible, for example, to add package information
(URL and DESCRIPTION) in the FindPackage file, but allow the package
to be RUNTIME.

Modules/FeatureSummary.cmake

@@ -439,24 +439,22 @@ function(SET_PACKAGE_PROPERTIES _name _props)
   endif()
 
   # handle the TYPE
-  if(NOT _SPP_TYPE)
-    set(_SPP_TYPE OPTIONAL)
-  endif()
-
-  # List the supported types, according to their priority
-  set(validTypes "RUNTIME" "OPTIONAL" "RECOMMENDED" "REQUIRED" )
-  list(FIND validTypes ${_SPP_TYPE} _typeIndexInList)
-  if("${_typeIndexInList}" STREQUAL "-1" )
-    message(FATAL_ERROR "Bad package property type ${_SPP_TYPE} used in SET_PACKAGE_PROPERTIES(). "
-                        "Valid types are OPTIONAL, RECOMMENDED, REQUIRED and RUNTIME." )
-  endif()
+  if(DEFINED _SPP_TYPE)
+    # List the supported types, according to their priority
+    set(validTypes "RUNTIME" "OPTIONAL" "RECOMMENDED" "REQUIRED" )
+    list(FIND validTypes ${_SPP_TYPE} _typeIndexInList)
+    if("${_typeIndexInList}" STREQUAL "-1" )
+      message(FATAL_ERROR "Bad package property type ${_SPP_TYPE} used in SET_PACKAGE_PROPERTIES(). "
+                          "Valid types are OPTIONAL, RECOMMENDED, REQUIRED and RUNTIME." )
+    endif()
 
-  get_property(_previousType  GLOBAL PROPERTY _CMAKE_${_name}_TYPE)
-  list(FIND validTypes "${_previousType}" _prevTypeIndexInList)
+    get_property(_previousType  GLOBAL PROPERTY _CMAKE_${_name}_TYPE)
+    list(FIND validTypes "${_previousType}" _prevTypeIndexInList)
 
-  # make sure a previously set TYPE is not overridden with a lower new TYPE:
-  if("${_typeIndexInList}" GREATER "${_prevTypeIndexInList}")
-    set_property(GLOBAL PROPERTY _CMAKE_${_name}_TYPE "${_SPP_TYPE}" )
+    # make sure a previously set TYPE is not overridden with a lower new TYPE:
+    if("${_typeIndexInList}" GREATER "${_prevTypeIndexInList}")
+      set_property(GLOBAL PROPERTY _CMAKE_${_name}_TYPE "${_SPP_TYPE}" )
+    endif()
   endif()
 
 endfunction()