use to_json and from_json in more places instead of encode_json and decode_json

lib/WebGUI/Asset/Wobject/Poll.pm

@@ -192,7 +192,7 @@ sub freezeGraphConfig {
     my $self        = shift;
     my $obj         = shift;
     
-    return JSON::encode_json($obj);
+    return JSON::to_json($obj);
 }
 
 
@@ -404,7 +404,7 @@ sub thawGraphConfig {
     my $string      = shift;
     
     return unless $string;
-    return JSON::decode_json($string);
+    return JSON::from_json($string);
 }
 
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