MLKEnvironment: Store [NSNull null] instead of nil.

1 files changed, 2 insertions, 0 deletions

diff --git a/MLKEnvironment.m b/MLKEnvironment.m
index 8488dd2..b2a3a81 100644
--- a/MLKEnvironment.m
+++ b/MLKEnvironment.m
@@ -69,6 +69,7 @@ static id UNBOUND;
 
 -(void) setBinding:(MLKSymbol *)symbol to:(id)value inEnvironment:(MLKEnvironment *)env
 {
+  value = value ? value : (id) [NSNull null];
   if ([_bindings objectForKey:symbol])
     [_bindings setObject:value forKey:symbol];
   else
@@ -117,6 +118,7 @@ static id UNBOUND;
 
 -(void) addValue:(id)value forBinding:(MLKSymbol *)symbol;
 {
+  value = value ? value : (id) [NSNull null];
   [_bindings setObject:value forKey:symbol];
 }