fix(mcp): ASCII chart crashes with NaN when dataset contains null values

superset/mcp_service/chart/ascii_charts.py

@@ -79,7 +79,11 @@ def _generate_ascii_bar_chart(data: list[Any], width: int, height: int) -> str:
             label_val = None
 
             for _key, val in row.items():
-                if isinstance(val, (int, float)) and numeric_val is None:
+                if (
+                    isinstance(val, (int, float))
+                    and not _is_nan_value(val)
+                    and numeric_val is None
+                ):
                     numeric_val = val
                 elif isinstance(val, str) and label_val is None:
                     label_val = val
@@ -121,7 +125,10 @@ def _generate_horizontal_bar_chart(
         # Calculate bar length
         if max_val > min_val:
             normalized = (value - min_val) / (max_val - min_val)
-            bar_length = max(1, int(normalized * max_bar_width))
+            if _is_nan_value(normalized):
+                bar_length = 0
+            else:
+                bar_length = max(1, int(normalized * max_bar_width))
         else:
             bar_length = 1
 
@@ -164,7 +171,10 @@ def _generate_vertical_bar_chart(  # noqa: C901
     for col, value in enumerate(values):
         if max_val > min_val:
             normalized = (value - min_val) / (max_val - min_val)
-            bar_height = max(1, int(normalized * chart_height))
+            if _is_nan_value(normalized):
+                bar_height = 0
+            else:
+                bar_height = max(1, int(normalized * chart_height))
         else:
             bar_height = 1
 
@@ -274,7 +284,11 @@ def _extract_time_series_data(data: list[Any]) -> tuple[list[float], list[str]]:
             label_val = None
 
             for key, val in row.items():
-                if isinstance(val, (int, float)) and numeric_val is None:
+                if (
+                    isinstance(val, (int, float))
+                    and not _is_nan_value(val)
+                    and numeric_val is None
+                ):
                     numeric_val = val
                 elif isinstance(val, str) and label_val is None:
                     # Use the key name if it looks like a date/time field

tests/unit_tests/mcp_service/chart/test_ascii_charts.py

@@ -0,0 +1,106 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+"""Unit tests for ascii_charts.py NaN/null value handling."""
+
+from superset.mcp_service.chart.ascii_charts import generate_ascii_chart
+
+
+def test_bar_chart_with_null_values_does_not_raise() -> None:
+    """Bar chart renderer must not crash when dataset rows contain NaN values."""
+    data = [
+        {"category": "A", "value": 10.0},
+        {"category": "B", "value": float("nan")},
+        {"category": "C", "value": 30.0},
+    ]
+    result = generate_ascii_chart(data, "bar")
+    assert isinstance(result, str)
+    assert len(result) > 0
+
+
+def test_bar_chart_with_all_null_values_returns_fallback() -> None:
+    """Bar chart with no valid numeric rows should return a fallback message."""
+    data = [
+        {"category": "A", "value": float("nan")},
+        {"category": "B", "value": float("nan")},
+    ]
+    result = generate_ascii_chart(data, "bar")
+    assert isinstance(result, str)
+    assert len(result) > 0
+
+
+def test_line_chart_with_null_values_does_not_raise() -> None:
+    """Line chart renderer must not crash when dataset rows contain NaN values."""
+    data = [
+        {"date": "2024-01", "sales": 100.0},
+        {"date": "2024-02", "sales": float("nan")},
+        {"date": "2024-03", "sales": 300.0},
+    ]
+    result = generate_ascii_chart(data, "line")
+    assert isinstance(result, str)
+    assert len(result) > 0
+
+
+def test_horizontal_bar_chart_nan_rows_are_skipped() -> None:
+    """NaN rows must be silently skipped; valid rows render normally."""
+    # Use labels longer than 8 chars to force horizontal layout, where full
+    # label text is preserved (vertical layout truncates to 3 chars).
+    data = [
+        {"label": "Alpha Category", "amount": 50.0},
+        {"label": "Beta Category", "amount": float("nan")},
+        {"label": "Gamma Category", "amount": 150.0},
+    ]
+    result = generate_ascii_chart(data, "bar")
+    # Valid labels should appear in output; NaN row should not crash
+    assert "Alpha" in result or "Gamma" in result
+
+
+def test_column_chart_with_null_values_does_not_raise() -> None:
+    """Column (vertical bar) chart must not crash on NaN values."""
+    data = [
+        {"x": "Q1", "y": 10.0},
+        {"x": "Q2", "y": float("nan")},
+        {"x": "Q3", "y": 30.0},
+        {"x": "Q4", "y": 40.0},
+    ]
+    result = generate_ascii_chart(data, "column")
+    assert isinstance(result, str)
+    assert len(result) > 0
+
+
+def test_timeseries_bar_with_null_values_does_not_raise() -> None:
+    """echarts_timeseries_bar chart type must not crash on NaN values."""
+    data = [
+        {"ts": "2024-01-01", "count": 5.0},
+        {"ts": "2024-01-02", "count": float("nan")},
+        {"ts": "2024-01-03", "count": 15.0},
+    ]
+    result = generate_ascii_chart(data, "echarts_timeseries_bar")
+    assert isinstance(result, str)
+    assert len(result) > 0
+
+
+def test_chart_with_none_values_does_not_raise() -> None:
+    """None (SQL NULL) values should be treated identically to NaN."""
+    data = [
+        {"name": "X", "metric": 100.0},
+        {"name": "Y", "metric": None},
+        {"name": "Z", "metric": 200.0},
+    ]
+    result = generate_ascii_chart(data, "bar")
+    assert isinstance(result, str)
+    assert len(result) > 0