Don't include useless/misleading "NULL" when dumping data from R .rdb files.

diffoscope/comparators/rdata.py

@@ -33,7 +33,8 @@ import binascii
 HEADER = binascii.a2b_hex("580a000000020003")
 
 DUMP_RDB = r"""
-lazyLoad(commandArgs(TRUE));
+hideOutput = lazyLoad(commandArgs(TRUE));
+
 for (obj in ls(all.names = TRUE, sorted = TRUE)) {
     print(obj);
     for (line in deparse(get(obj)))