Fix Dropdown placeholder error - remove invalid placeholder argument

app.py

@@ -125,25 +125,25 @@ with gr.Blocks(title="Organic Reactions Search") as demo:
     gr.Markdown("Search through the organic reactions dataset by name, reactant, or product.")
 
     with gr.Tab("Search by Reaction Name"):
-        reaction_input = gr.Dropdown(label="Reaction Name", choices=reaction_names, allow_custom_value=True, placeholder="Type or select a reaction name")
+        reaction_input = gr.Dropdown(label="Reaction Name", choices=reaction_names, allow_custom_value=True)
         reaction_output = gr.Markdown(label="Result")
         reaction_btn = gr.Button("Search")
         reaction_btn.click(search_by_reaction_name, inputs=reaction_input, outputs=reaction_output)
 
     with gr.Tab("Search by Reactant"):
-        reactant_input = gr.Dropdown(label="Reactant", choices=unique_reactants, allow_custom_value=True, placeholder="Type or select a reactant")
+        reactant_input = gr.Dropdown(label="Reactant", choices=unique_reactants, allow_custom_value=True)
         reactant_output = gr.Markdown(label="Results")
         reactant_btn = gr.Button("Search")
         reactant_btn.click(search_by_reactant, inputs=reactant_input, outputs=reactant_output)
 
     with gr.Tab("View Reaction SVG"):
-        svg_input = gr.Dropdown(label="Reaction Name", choices=reaction_names, allow_custom_value=True, placeholder="Type or select a reaction name")
+        svg_input = gr.Dropdown(label="Reaction Name", choices=reaction_names, allow_custom_value=True)
         svg_output = gr.HTML(label="Reaction SVG")
         svg_btn = gr.Button("Generate SVG")
         svg_btn.click(generate_reaction_svg, inputs=svg_input, outputs=svg_output)
 
     with gr.Tab("Search by Product"):
-        product_input = gr.Dropdown(label="Product", choices=unique_products, allow_custom_value=True, placeholder="Type or select a product")
+        product_input = gr.Dropdown(label="Product", choices=unique_products, allow_custom_value=True)
         product_output = gr.Markdown(label="Results")
         product_btn = gr.Button("Search")
         product_btn.click(search_by_product, inputs=product_input, outputs=product_output)