在搭建深度学习模型的时候使用到

context_ = layers.assign(context)

但是执行exe.run的时候报了如下错误：

Error: The Input Variable(X) of assign Op used to determine kernel data type is empty or not LoDTensor or SelectedRows.
[Hint: Expected data_type != dafault_data_type, but received data_type:-1 == dafault_data_type:-1.] at (D:\1.6.3\paddle\paddle\fluid\framework\operator.cc:1181)

这是context的属性：

name: "tmp_84"
type {
type: LOD_TENSOR
lod_tensor {
tensor {
data_type: FP32
dims: -1
dims: 300
dims: 256
}
lod_level: 0
}
}

请问怎么解决这个错误呀？