patch 9.1.0387: Vim9: null value tests not sufficient

Problem:  Vim9: null value tests not sufficient
Solution: Add a more comprehensive test for null values
          (Yegappan Lakshmanan)

closes: #14701

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 742c5f8..8ee5cbd 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3958,7 +3958,7 @@
 					  || *argvars[0].vval.v_string == NUL;
 	    break;
 	case VAR_PARTIAL:
-	    n = FALSE;
+	    n = argvars[0].vval.v_partial == NULL;
 	    break;
 	case VAR_NUMBER:
 	    n = argvars[0].vval.v_number == 0;
@@ -11497,7 +11497,7 @@
 	case VAR_CLASS:
 	    {
 		class_T *cl = argvars[0].vval.v_class;
-		if (cl && IS_ENUM(cl))
+		if (cl != NULL && IS_ENUM(cl))
 		    n = VAR_TYPE_ENUM;
 		else
 		    n = VAR_TYPE_CLASS;