diff -ur v5/ezyaml.py v6/ezyaml.py
--- v5/ezyaml.py	2018-08-31 05:15:00.000000000 +0900
+++ v6/ezyaml.py	2018-08-31 22:53:33.000000000 +0900
@@ -201,6 +201,17 @@
 		lines.append(s)
 	return '\n'.join(lines)
 
+def need_quote(s):
+	kwd = [ '', 'True', 'true', 'TRUE', 'False', 'false', 'FALSE', 'ON', 'On', 'on', 'OFF', 'Off', 'off' ]
+	if s in kwd:
+		return True
+
+	hts = [ ('[', ']'), ('{', '}') ]
+	if ( s[:1], s[-1:] ) in hts:
+		return True	
+
+	return False
+
 def dump_value(obj):
 	if type(obj) == str:
 		s = obj
@@ -208,7 +219,7 @@
 		if q2 and q1:
 			s = s.replace("'", "\\'")
 			q1 = False
-		if q2 or q1 or cl or get_value(s) != obj or s == '':
+		if q2 or q1 or cl or get_value(s) != obj or need_quote(s):
 			qt = '"' if q1 else "'"
 			s = qt + s + qt
 		return s
@@ -219,6 +230,9 @@
 	if type(obj) == dict:
 		return '{}'
 
+	if obj == None:
+		return 'null'
+
 	return '{}'.format(obj)
 
 def dump_other(obj, idt):