Don't set chart if it is None

Author: forman

chartlets.py/chartlets/components/plot.py

@@ -12,16 +12,13 @@ class Plot(Component):
     [Vega Altair](https://altair-viz.github.io/) chart."""
 
     theme: str | None = None
-    """A [Vega theme name](https://vega.github.io/vega-themes/)."""
+    """The name of a [Vega theme](https://vega.github.io/vega-themes/)."""
 
     chart: alt.Chart | None = None
-    """The Vega Altair 
-    [chart object](https://altair-viz.github.io/user_guide/generated/toplevel/altair.Chart.html)."""
+    """The [Vega Altair chart](https://altair-viz.github.io/gallery/index.html)."""
 
     def to_dict(self) -> dict[str, Any]:
         d = super().to_dict()
         if self.chart is not None:
             d.update(chart=self.chart.to_dict())
-        else:
-            d.update(chart=None)
         return d

chartlets.py/tests/components/plot_test.py

@@ -1,6 +1,3 @@
-import json
-import unittest
-
 import pandas as pd
 import altair as alt
 
@@ -12,7 +9,7 @@
 
 class PlotTest(make_base(Plot)):
 
-    def test_is_json_serializable(self):
+    def test_with_chart(self):
         source = pd.DataFrame(
             {"x": ["A", "B", "C", "D", "E"], "a": [28, 55, 43, 91, 81]}
         )
@@ -28,6 +25,8 @@ def test_is_json_serializable(self):
         self.assert_is_json_serializable(
             self.cls(id="plot", theme="dark", chart=self.chart),
             {
+                "type": "Plot",
+                "id": "plot",
                 "theme": "dark",
                 "chart": {
                     "$schema": "https://vega.github.io/schema/vega-lite/v5.20.1.json",
@@ -50,7 +49,11 @@ def test_is_json_serializable(self):
                     },
                     "mark": {"type": "bar"},
                 },
-                "id": "plot",
-                "type": "Plot",
             },
         )
+
+    def test_without_chart(self):
+        self.assert_is_json_serializable(
+            self.cls(id="plot", style={"width": 100}),
+            {"type": "Plot", "id": "plot", "style": {"width": 100}},
+        )