fix None errors

app.py

@@ -16,7 +16,8 @@ def generate_prompt(instruction, input=None, history=None):
     # parse the chat history into a string of user and assistant messages
     history_str = ""
 
-    if history is not None:
+    has_history = (history is not None)
+    if has_history:
         for pair in history:
             history_str += f"User: {pair[0]}\n\nAssistant: {pair[1]}\n\n"
 
@@ -26,10 +27,14 @@ def generate_prompt(instruction, input=None, history=None):
         .replace("\n\n", "\n")
         .replace("\n\n", "\n")
     )
-    input = (
-        input.strip().replace("\r\n", "\n").replace("\n\n", "\n").replace("\n\n", "\n")
-    )
-    if input and len(input) > 0:
+    if not has_history:
+        input = (
+            input.strip()
+            .replace("\r\n", "\n")
+            .replace("\n\n", "\n")
+            .replace("\n\n", "\n")
+        )
+    if not has_history and len(input) > 0:
         return f"""{history_str}Instruction: {instruction}
 
 Input: {input}