Show error if user tries to plot with no data

src/frames/stats_frame.py

@@ -1,5 +1,6 @@
 import customtkinter as ctk
 from datetime import datetime
+from CTkMessagebox import CTkMessagebox
 from src.reusable.stats_reusable import StatisticFrame, ButtonFrame
 from src.utils import load_data
 from src.logic.graphs import graph_pomodoro_sessions, graph_hours_studied
@@ -51,8 +52,20 @@ def update_total_pomodoros(self, data):
         total_pomodoros = data.get('total_pomodoro_sessions', 0)
         self.total_pomodoros.set_value(f"{total_pomodoros} session{'s' if total_pomodoros != 1 else ''}")
 
+    def _ensure_exists(self, param, msg):
+        data = load_data()
+        value = data.get(param, 0)
+        if value == 0:
+            CTkMessagebox(title="Error", message=msg, icon="cancel")
+            return False
+        return True
+
     def show_sessions_graph(self):
+        if not self._ensure_exists('total_pomodoro_sessions', 'Cannot graph pomodoro sessions: none recorded'):
+            return
         graph_pomodoro_sessions(load_data())
 
     def show_hours_graph(self):
+        if not self._ensure_exists('total_seconds_studied', 'Cannot graph hours studied: none recorded'):
+            return
         graph_hours_studied(load_data())