memory (sqla): don't set keys with None as value for RSM in getItems

sat/memory/sqla.py

@@ -1365,12 +1365,13 @@ class Storage:
             else:
                 last = result[-1][1].name
 
-
             metadata["rsm"] = {
-                "index": index,
-                "count": rows_count,
-                "first": first,
-                "last": last,
+                k: v for k, v in {
+                    "index": index,
+                    "count": rows_count,
+                    "first": first,
+                    "last": last,
+                }.items() if v is not None
             }
             metadata["complete"] = index + len(result) == rows_count