title: PyG: RuntimeError: Tensors must have same number of dimensions: got 2 and 3
body: <p>I am using <code>TransformerConv</code> and encountered this error:</p>
  <pre><code>Traceback (most recent call last):
  
  File &quot;pipeline_model_gat.py&quot;, line 1018, in &lt;module&gt;
  output = model( 
  File&quot;/mount/arbeitsdaten61/studenten3/advanced-ml/2022/gogirlspower/nicole/conda/envs/new_gvqa/lib/python3.8/sitepackages/torch/nn/modules/module.py&quot;, line 727, in _call_impl
  result = self.forward(*input, **kwargs)
  File &quot;pipeline_model_gat.py&quot;, line 881, in forwardquestions_encoded = self.question_encoder(question_graphs)  
  File &quot;/mount/arbeitsdaten61/studenten3/advanced-ml/2022/gogirlspower/nicole/conda/envs/new_gvqa/lib/python3.8/site-packages/torch/nn/modules/module.py&quot;, line 727, in _call_impl
  result = self.forward(*input, **kwargs)
  File &quot;pipeline_model_gat.py&quot;, line 628, in forward= self.conv1(x, question_graphs.edge_index, edge_attr)  
  File &quot;/mount/arbeitsdaten61/studenten3/advanced-ml/2022/gogirlspower/nicole/conda/envs/new_gvqa/lib/python3.8/site-packages/torch/nn/modules/module.py&quot;, line 727, in _call_impl
  result = self.forward(*input, **kwargs) 
  File &quot;/mount/arbeitsdaten61/studenten3/advanced-ml/2022/gogirlspower/nicole/conda/envs/new_gvqa/lib/python3.8/site-packages/torch_geometric/nn/conv/transformer_conv.py&quot;, line 190, in forward
  beta = self.lin_beta(torch.cat([out, x_r, out - x_r], dim=-1))
  RuntimeError: Tensors must have same number of dimensions: got 2 and 3 
  </code></pre>
  <p>Can someone please tell me what could have gone wrong?</p>