docstr: Convert a node to tensor
docstr_tok: ["Convert","a","node","to","tensor"]
code: def to_tensor(self):
      """
      Convert a node to tensor
      """
      out_tensor = self._to_tensor()
      if self.node_name:
          out_tensor.set_name(self.node_name)
      assert isinstance(out_tensor, zautograd.Variable) or isinstance(
          out_tensor, zautograd.Parameter
      )
      if self.model_trainable_values:
          out_tensor.node.element().set_weights(
              self.to_zoo_format(self.model_trainable_values)
          )
      return out_tensor
  
file_path: analytics-zoo/pyzoo/zoo/pipeline/api/onnx/mapper/operator_mapper.py
imports: import zoo.pipeline.api.keras.layers
  import zoo.pipeline.api.autograd
  from zoo.pipeline.api.onnx.onnx_helper import OnnxHelper
  import zoo.pipeline.api.onnx.mapper
  import importlib
  import numpy
label_desc: Use image node_id 4 for calling the OperatorMapper obj's underlying member method code with example usage: obj.to_tensor() and returns: out_tensor