docs(examples): add point_label_null examples

Author: kanitw

examples/specs/point_label_null.vl.json

@@ -0,0 +1,26 @@
+{
+  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
+  "data": {
+    "values": [
+      {"a": "Jan 1, 2000", "b": 28},
+      {"a": "Jan 2, 2000", "b": 55},
+      {"a": "Jan 3, 2000", "b": null},
+      {"a": "Jan 4, 2000", "b": 65},
+      {"a": "Jan 5, 2000", "b": 43},
+      {"a": null, "b": 50}
+    ]
+  },
+
+  "encoding": {
+    "x": {"timeUnit": "yearmonthdate", "field": "a", "type": "temporal", "axis": {"format": "%d %b"}},
+    "y": {"field": "b", "type": "quantitative"}
+  },
+  "layer": [{
+    "mark": {"type": "point", "invalid": "show"}
+  }, {
+    "mark": {"type": "text", "invalid": "show", "baseline": "bottom"},
+    "encoding": {
+      "text": {"field": "b", "type": "quantitative"}
+    }
+  }]
+}

examples/specs/point_label_null_date.vl.json

@@ -0,0 +1,29 @@
+{
+  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
+  "data": {
+    "values": [
+      {"a": "Jan 1, 2000", "b": 28},
+      {"a": "Jan 2, 2000", "b": 55},
+      {"a": "Jan 3, 2000", "b": null},
+      {"a": "Jan 4, 2000", "b": 65},
+      {"a": "Jan 5, 2000", "b": 43},
+      {"a": null, "b": 50}
+    ]
+  },
+
+  "encoding": {
+    "x": {"timeUnit": "yearmonthdate", "field": "a", "type": "temporal", "axis": {"format": "%d %b"}},
+    "y": {"field": "b", "type": "quantitative"}
+  },
+  "layer": [{
+    "mark": {"type": "point", "invalid": "show", "tooltip": true},
+    "encoding": {
+      "x": {"timeUnit": "yearmonthdate", "field": "a", "type": "temporal"}
+    }
+  }, {
+    "mark": {"type": "text", "invalid": "show", "baseline": "bottom"},
+    "encoding": {
+      "text": {"timeUnit": "yearmonthdate", "field": "a", "type": "temporal", "axis": {"format": "%d %b"}}
+    }
+  }]
+}