Error occurred when executing Simple String Combine (WLSH): can only concatenate str (not "list") to str

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Error occurred when executing Simple String Combine (WLSH):

can only concatenate str (not "list") to str

File "/workspace/ComfyUI/execution.py", line 151, in recursive_execute
output_data, output_ui = get_output_data(obj, input_data_all)
File "/workspace/ComfyUI/execution.py", line 81, in get_output_data
return_values = map_node_over_list(obj, input_data_all, obj.FUNCTION, allow_interrupt=True)
File "/workspace/ComfyUI/execution.py", line 74, in map_node_over_list
results.append(getattr(obj, func)(**slice_dict(input_data_all, i)))
File "/workspace/ComfyUI/custom_nodes/wlsh_nodes/wlsh_nodes.py", line 409, in concat_string
new_string = input_string + sep[separator] + addition