self.alpha = bpyNode.image.file_format not in NON_ALPHA_FORMATS

` super().__init__(bpyNode, socketName, overloadChannels)
File "C:\Users\sheng\AppData\Roaming\Blender Foundation\Blender\2.93\scripts\addons\babylon_js\materials\nodes\abstract.py", line 84, in __init__
bjsWrapperNode = AbstractBJSNode.GetBJSWrapperNode(nodeSocket.links[0].from_node, nodeSocket.name, overloadChannels)
File "C:\Users\sheng\AppData\Roaming\Blender Foundation\Blender\2.93\scripts\addons\babylon_js\materials\nodes\abstract.py", line 356, in GetBJSWrapperNode
return UnsupportedNode(bpyNode, socketName, overloadChannels)
File "C:\Users\sheng\AppData\Roaming\Blender Foundation\Blender\2.93\scripts\addons\babylon_js\materials\nodes\unsupported.py", line 12, in __init__
super().__init__(bpyNode, socketName, overloadChannels)
File "C:\Users\sheng\AppData\Roaming\Blender Foundation\Blender\2.93\scripts\addons\babylon_js\materials\nodes\abstract.py", line 84, in __init__
bjsWrapperNode = AbstractBJSNode.GetBJSWrapperNode(nodeSocket.links[0].from_node, nodeSocket.name, overloadChannels)
File "C:\Users\sheng\AppData\Roaming\Blender Foundation\Blender\2.93\scripts\addons\babylon_js\materials\nodes\abstract.py", line 347, in GetBJSWrapperNode
return TextureImageBJSNode(bpyNode, socketName, overloadChannels)
File "C:\Users\sheng\AppData\Roaming\Blender Foundation\Blender\2.93\scripts\addons\babylon_js\materials\nodes\tex_image.py", line 13, in __init__
self.alpha = bpyNode.image.file_format not in NON_ALPHA_FORMATS`

Start with materials/nodes/tex_image.py at line 13, then trace the construction path through materials/nodes/abstract.py lines 84 and 347-356 and materials/nodes/unsupported.py line 12. Reproduce the reported export failure with the same kind of node setup and determine the expected behavior; done means the export no longer reaches this traceback.

Written by the indexing model from the issue text.