Print message if there isn't an API key pasted

app.py

@@ -43,6 +43,9 @@ def openai_create(prompt, openai_api_key):
 
 
 def calc_gpt_only(math_problem, openai_api_key):
+    if not openai_api_key or openai_api_key == "":
+        return "<pre>Please paste your OpenAI API key</pre>"
+
     answer = openai_create(gpt_only_prompt + math_problem + "\n", openai_api_key)
 
     print("\n==== date/time: " + str(datetime.datetime.now()) + " ====")
@@ -54,6 +57,9 @@ def calc_gpt_only(math_problem, openai_api_key):
 
 
 def calc_gpt_pal(math_problem, pal_chain):
+    if not pal_chain:
+        return "<pre>Please paste your OpenAI API key</pre>"
+
     answer = pal_chain.run(math_problem)
 
     print("\n==== date/time: " + str(datetime.datetime.now()) + " ====")