diff --git a/app/ptxboa_functions.py b/app/ptxboa_functions.py
index 86ecd54b..08154b94 100644
--- a/app/ptxboa_functions.py
+++ b/app/ptxboa_functions.py
@@ -3,6 +3,7 @@
 from pathlib import Path
 from typing import Literal
 
+import numpy as np
 import pandas as pd
 import streamlit as st
 
@@ -447,7 +448,9 @@ def register_user_changes(
     columns: str,
     values: str,
     df_tab: pd.DataFrame,
+    df_orig: pd.DataFrame,
     key: str,
+    editor_key: str,
 ):
     """
     Register all user changes in the session state variable "user_changes_df".
@@ -456,13 +459,29 @@ def register_user_changes(
     """
     # convert session state dict to dataframe:
     # Create a list of dictionaries
-    data_dict = st.session_state[key]["edited_rows"]
+    data_dict = st.session_state[editor_key]["edited_rows"]
     if any(data_dict):
         data_list = []
 
+        rejected_changes = False
         for k, v in data_dict.items():
             for c_name, value in v.items():
-                data_list.append({index: k, columns: c_name, values: value})
+                if np.isnan(df_orig.iloc[k, :][c_name]):
+                    msg = (
+                        f":exclamation: Cannot modify empty value '{c_name}' "
+                        f"for '{df_orig.index[k]}'"
+                    )
+                    st.toast(msg)
+                    rejected_changes = True
+                else:
+                    data_list.append({index: k, columns: c_name, values: value})
+
+        if rejected_changes:
+            # modify key number
+            st.session_state[f"{key}_number"] += 1
+
+        if len(data_list) == 0:
+            return
 
         # Convert the list to a DataFrame
         res = pd.DataFrame(data_list)
@@ -544,13 +563,28 @@ def display_and_edit_input_data(
         data type "conversion_processes" and "transportation_processes" which is not
         region specific.
     key : str
-        A key for the data editing streamlit widget. Need to be unique.
+        A key for the data editing layout element. Needs to be unique in the app.
+        Several session state variables are derived from this key::
+
+            - st.session_state[f"{key}_number"]:
+                This is initialized with 0 and incremented by 1 whenever any input
+                value got rejected by the callback function
+                :func:`register_user_changes`. This will trigger a re-rendering of the
+                data_editor widget and thus reset modifications on empty values.
+            - st.session_state[f"{key}_form"]:
+                the key for the form the editor lives in
+            - st_session_state[f"{key}_{st.session_state[f'{key}_number']}"]:
+                the name of this session state variable consists of the `key` and the
+                current `{key}_number`. It refers to the st.data_editor widget.
+                Whenever the key_number changes, the editor widget gets a new key and
+                is initialized from scratch.
 
     Returns
     -------
     pd.DataFrame
     """
     df = get_data_type_from_input_data(api, data_type=data_type, scope=scope)
+    df_orig = df.copy()
 
     if data_type in [
         "electricity_generation",
@@ -605,6 +639,10 @@ def display_and_edit_input_data(
 
     # if editing is enabled, store modifications in session_state:
     if st.session_state["edit_input_data"]:
+        if f"{key}_number" not in st.session_state:
+            st.session_state[f"{key}_number"] = 0
+        editor_key = f"{key}_{st.session_state[f'{key}_number']}"
+
         with st.form(key=f"{key}_form"):
             st.info(
                 (
@@ -613,17 +651,10 @@ def display_and_edit_input_data(
                 )
             )
 
-            if df.isna().any().any():
-                # TODO: remove this warning when input data is fixed.
-                msg = (
-                    "Draft version: Do no edit empty data points (None), this will "
-                    "throw an error. Missing data has to be filled before publishing."
-                )
-                st.warning(msg)
             df = st.data_editor(
                 df,
                 use_container_width=True,
-                key=key,
+                key=editor_key,
                 num_rows="fixed",
                 disabled=[index],
                 column_config=column_config,
@@ -639,7 +670,9 @@ def display_and_edit_input_data(
                     "columns": columns,
                     "values": "value",
                     "df_tab": df,
+                    "df_orig": df_orig,
                     "key": key,
+                    "editor_key": editor_key,
                 },
             )
     else: