changed validation for stirring speed

app.py

@@ -160,7 +160,7 @@ if st.session_state["experiment"] is not None:
     st.header("Stirring")
     if st.session_state["jobs"]["stirring"]:
         with st.form("stirring_form"):
-            if "stirring_speed" not in st.session_state:
+            if st.session_state.get("stirring_speed", None) is None:
                 st.write("Current Stirring Speed Unknown")
             else:
                 st.write(f"Current Stirring Speed: {st.session_state['stirring_speed']} RPM")