Fix ONNX browser attribute values

src/netron.py

@@ -106,7 +106,7 @@ class OnnxModel:
             self.remove_tensor_data(initializer)
         for node in model.graph.node:
             for attribute in node.attribute:
-                if attribute.t:
+                if attribute.HasField('t'):
                     self.remove_tensor_data(attribute.t)
         self.data = model.SerializeToString()
     def remove_tensor_data(self, tensor):
@@ -114,7 +114,7 @@ class OnnxModel:
         del tensor.int32_data[:]
         del tensor.int64_data[:]
         del tensor.float_data[:]
-        tensor.raw_data = b''
+        tensor.raw_data = None
 
 class TensorFlowLiteModel:
     def __init__(self, data, file):