patch 7.4.1755
Problem:    When using getreg() on a non-existing register a NULL list is
            returned. (Bjorn Linse)
Solution:   Allocate an empty list. Add a test.
diff --git a/src/eval.c b/src/eval.c
index bd4a11a..28cc2f1 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -6051,7 +6051,7 @@
 }
 
 /*
- * Allocate an empty list for a return value.
+ * Allocate an empty list for a return value, with reference count set.
  * Returns OK or FAIL.
  */
     int
@@ -13173,7 +13173,9 @@
 	rettv->v_type = VAR_LIST;
 	rettv->vval.v_list = (list_T *)get_reg_contents(regname,
 				      (arg2 ? GREG_EXPR_SRC : 0) | GREG_LIST);
-	if (rettv->vval.v_list != NULL)
+	if (rettv->vval.v_list == NULL)
+	    rettv_list_alloc(rettv);
+	else
 	    ++rettv->vval.v_list->lv_refcount;
     }
     else