added unit test for json_value_add_null.

minor correction to json_value_validate: error_msg should have been intent(out)

Author: jacobwilliams

files/inputs/test2.json

@@ -19,7 +19,8 @@
       true,
       false,
       true
-    ]
+    ],
+    "null_variable": null
   },
   "trajectory": [
     {

src/json_value_module.F90

@@ -1945,8 +1945,8 @@ subroutine json_value_validate(json,p,is_valid,error_msg)
     class(json_core),intent(inout)       :: json
     type(json_value),pointer,intent(in)  :: p
     logical(LK),intent(out)              :: is_valid  !! True if the structure is valid.
-    character(kind=CK,len=:),allocatable :: error_msg !! if not valid, this will contain
-                                                      !! a description of the problem
+    character(kind=CK,len=:),allocatable,intent(out) :: error_msg !! if not valid, this will contain
+                                                                  !! a description of the problem
 
     if (associated(p)) then
         is_valid = .true.

src/tests/jf_test_2.f90

@@ -133,6 +133,11 @@ subroutine test_2(error_cnt)
         call json%print_error_message(error_unit)
         error_cnt = error_cnt + 1
     end if
+    call json%add(inp, 'null_variable')
+    if (json%failed()) then
+        call json%print_error_message(error_unit)
+        error_cnt = error_cnt + 1
+    end if
     nullify(inp)
 
     !trajectory variables: