diff --git a/lib/yaml/__init__.py b/lib/yaml/__init__.py
index 8780663c..7622218c 100644
--- a/lib/yaml/__init__.py
+++ b/lib/yaml/__init__.py
@@ -251,7 +251,7 @@ def serialize(node, stream=None, Dumper=Dumper, **kwds):
     return serialize_all([node], stream, Dumper=Dumper, **kwds)
 
 def dump_all(documents, stream=None, Dumper=Dumper,
-        default_style=None, default_flow_style=None,
+        default_style=None, default_flow_style=False,
         canonical=None, indent=None, width=None,
         allow_unicode=None, line_break=None,
         encoding='utf-8', explicit_start=None, explicit_end=None,
diff --git a/lib/yaml/cyaml.py b/lib/yaml/cyaml.py
index 648c34f4..ebb89593 100644
--- a/lib/yaml/cyaml.py
+++ b/lib/yaml/cyaml.py
@@ -51,7 +51,7 @@ def __init__(self, stream):
 class CBaseDumper(CEmitter, BaseRepresenter, BaseResolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -68,7 +68,7 @@ def __init__(self, stream,
 class CSafeDumper(CEmitter, SafeRepresenter, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -85,7 +85,7 @@ def __init__(self, stream,
 class CDumper(CEmitter, Serializer, Representer, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
diff --git a/lib/yaml/dumper.py b/lib/yaml/dumper.py
index 6fa7855d..f9cd49fd 100644
--- a/lib/yaml/dumper.py
+++ b/lib/yaml/dumper.py
@@ -9,7 +9,7 @@
 class BaseDumper(Emitter, Serializer, BaseRepresenter, BaseResolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -27,7 +27,7 @@ def __init__(self, stream,
 class SafeDumper(Emitter, Serializer, SafeRepresenter, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -45,7 +45,7 @@ def __init__(self, stream,
 class Dumper(Emitter, Serializer, Representer, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
diff --git a/lib/yaml/representer.py b/lib/yaml/representer.py
index 3432cc7e..9dca41af 100644
--- a/lib/yaml/representer.py
+++ b/lib/yaml/representer.py
@@ -17,7 +17,7 @@ class BaseRepresenter(object):
     yaml_representers = {}
     yaml_multi_representers = {}
 
-    def __init__(self, default_style=None, default_flow_style=None, sort_keys=True):
+    def __init__(self, default_style=None, default_flow_style=False, sort_keys=True):
         self.default_style = default_style
         self.default_flow_style = default_flow_style
         self.sort_keys = sort_keys
diff --git a/lib3/yaml/__init__.py b/lib3/yaml/__init__.py
index 004c5b8d..d4194ccd 100644
--- a/lib3/yaml/__init__.py
+++ b/lib3/yaml/__init__.py
@@ -249,7 +249,7 @@ def serialize(node, stream=None, Dumper=Dumper, **kwds):
     return serialize_all([node], stream, Dumper=Dumper, **kwds)
 
 def dump_all(documents, stream=None, Dumper=Dumper,
-        default_style=None, default_flow_style=None,
+        default_style=None, default_flow_style=False,
         canonical=None, indent=None, width=None,
         allow_unicode=None, line_break=None,
         encoding=None, explicit_start=None, explicit_end=None,
diff --git a/lib3/yaml/cyaml.py b/lib3/yaml/cyaml.py
index 66217f25..1e606c74 100644
--- a/lib3/yaml/cyaml.py
+++ b/lib3/yaml/cyaml.py
@@ -51,7 +51,7 @@ def __init__(self, stream):
 class CBaseDumper(CEmitter, BaseRepresenter, BaseResolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -68,7 +68,7 @@ def __init__(self, stream,
 class CSafeDumper(CEmitter, SafeRepresenter, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -85,7 +85,7 @@ def __init__(self, stream,
 class CDumper(CEmitter, Serializer, Representer, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
diff --git a/lib3/yaml/dumper.py b/lib3/yaml/dumper.py
index b17ffa30..6aadba55 100644
--- a/lib3/yaml/dumper.py
+++ b/lib3/yaml/dumper.py
@@ -9,7 +9,7 @@
 class BaseDumper(Emitter, Serializer, BaseRepresenter, BaseResolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -27,7 +27,7 @@ def __init__(self, stream,
 class SafeDumper(Emitter, Serializer, SafeRepresenter, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
@@ -45,7 +45,7 @@ def __init__(self, stream,
 class Dumper(Emitter, Serializer, Representer, Resolver):
 
     def __init__(self, stream,
-            default_style=None, default_flow_style=None,
+            default_style=None, default_flow_style=False,
             canonical=None, indent=None, width=None,
             allow_unicode=None, line_break=None,
             encoding=None, explicit_start=None, explicit_end=None,
diff --git a/lib3/yaml/representer.py b/lib3/yaml/representer.py
index 2f230bb8..dd144017 100644
--- a/lib3/yaml/representer.py
+++ b/lib3/yaml/representer.py
@@ -15,7 +15,7 @@ class BaseRepresenter:
     yaml_representers = {}
     yaml_multi_representers = {}
 
-    def __init__(self, default_style=None, default_flow_style=None, sort_keys=True):
+    def __init__(self, default_style=None, default_flow_style=False, sort_keys=True):
         self.default_style = default_style
         self.sort_keys = sort_keys
         self.default_flow_style = default_flow_style