Session with only null state yields uncompilable code

[senier]

package Test is
   generic
   session S with
      Initial => Done,
      Final   => Done
   is
   begin
      state Done is null state;
   end S;
end Test;

$ gprbuild 
using project file /opt/GNAT-Community-2021/share/gpr/_default.gpr
Compile
   [Ada]          rflx-test-s_allocator.adb
rflx-test-s_allocator.adb:22:03: error: statement expected
gprbuild: *** compilation phase failed

package body RFLX.Test.S_Allocator with                                                                                 
  SPARK_Mode                                                                                                            
is                                                                                                                                                          
                                                                                                                        
   procedure Initialize with                                                                                            
     SPARK_Mode =>                                                                                                      
       Off                                                                                                              
   is                                                                                                                   
   begin                                                                                                                
                                                                                                                        
   end Initialize;                                                                                                      
                                                                                                                        
end RFLX.Test.S_Allocator;