We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Dots aren't showing up in ranged dot plot
![Screenshot from 2022-06-30 20-02-14](https://user-images.githubusercontent.com/9993/176815294-a1801b76-ed5a-4f3c-b38f-71850c131a5a.png)


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `altair/examples/ranged_dot_plot.py`
Content:
```
1 """
2 Ranged Dot Plot
3 -----------------
4 This example shows a ranged dot plot that uses 'layer' to convey changing life expectancy for the five most populous countries (between 1955 and 2000).
5 """
6 # category: other charts
7 import altair as alt
8 from vega_datasets import data
9 
10 source = data.countries.url
11 
12 chart = alt.layer(
13     data=source
14 ).transform_filter(
15     filter={"field": 'country',
16             "oneOf": ["China", "India", "United States", "Indonesia", "Brazil"]}
17 ).transform_filter(
18     filter={'field': 'year',
19             "oneOf": [1955, 2000]}
20 )
21 
22 chart += alt.Chart().mark_line(color='#db646f').encode(
23     x='life_expect:Q',
24     y='country:N',
25     detail='country:N'
26 )
27 # Add points for life expectancy in 1955 & 2000
28 chart += alt.Chart().mark_point(
29     size=100,
30     opacity=1,
31     filled=True
32 ).encode(
33     x='life_expect:Q',
34     y='country:N',
35     color=alt.Color('year:O',
36         scale=alt.Scale(
37             domain=['1955', '2000'],
38             range=['#e6959c', '#911a24']
39         )
40     )
41 ).interactive()
42 
43 chart
44
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/altair/examples/ranged_dot_plot.py b/altair/examples/ranged_dot_plot.py
--- a/altair/examples/ranged_dot_plot.py
+++ b/altair/examples/ranged_dot_plot.py
@@ -1,7 +1,7 @@
 """
 Ranged Dot Plot
------------------
-This example shows a ranged dot plot that uses 'layer' to convey changing life expectancy for the five most populous countries (between 1955 and 2000).
+---------------
+This example shows a ranged dot plot to convey changing life expectancy for the five most populous countries (between 1955 and 2000).
 """
 # category: other charts
 import altair as alt
@@ -9,7 +9,7 @@
 
 source = data.countries.url
 
-chart = alt.layer(
+chart = alt.Chart(
     data=source
 ).transform_filter(
     filter={"field": 'country',
@@ -19,13 +19,13 @@
             "oneOf": [1955, 2000]}
 )
 
-chart += alt.Chart().mark_line(color='#db646f').encode(
+line = chart.mark_line(color='#db646f').encode(
     x='life_expect:Q',
     y='country:N',
     detail='country:N'
 )
 # Add points for life expectancy in 1955 & 2000
-chart += alt.Chart().mark_point(
+points = chart.mark_point(
     size=100,
     opacity=1,
     filled=True
@@ -34,10 +34,10 @@
     y='country:N',
     color=alt.Color('year:O',
         scale=alt.Scale(
-            domain=['1955', '2000'],
+            domain=[1955, 2000],
             range=['#e6959c', '#911a24']
         )
     )
 ).interactive()
 
-chart
+(line + points)

{"golden_diff": "diff --git a/altair/examples/ranged_dot_plot.py b/altair/examples/ranged_dot_plot.py\n--- a/altair/examples/ranged_dot_plot.py\n+++ b/altair/examples/ranged_dot_plot.py\n@@ -1,7 +1,7 @@\n \"\"\"\n Ranged Dot Plot\n------------------\n-This example shows a ranged dot plot that uses 'layer' to convey changing life expectancy for the five most populous countries (between 1955 and 2000).\n+---------------\n+This example shows a ranged dot plot to convey changing life expectancy for the five most populous countries (between 1955 and 2000).\n \"\"\"\n # category: other charts\n import altair as alt\n@@ -9,7 +9,7 @@\n \n source = data.countries.url\n \n-chart = alt.layer(\n+chart = alt.Chart(\n     data=source\n ).transform_filter(\n     filter={\"field\": 'country',\n@@ -19,13 +19,13 @@\n             \"oneOf\": [1955, 2000]}\n )\n \n-chart += alt.Chart().mark_line(color='#db646f').encode(\n+line = chart.mark_line(color='#db646f').encode(\n     x='life_expect:Q',\n     y='country:N',\n     detail='country:N'\n )\n # Add points for life expectancy in 1955 & 2000\n-chart += alt.Chart().mark_point(\n+points = chart.mark_point(\n     size=100,\n     opacity=1,\n     filled=True\n@@ -34,10 +34,10 @@\n     y='country:N',\n     color=alt.Color('year:O',\n         scale=alt.Scale(\n-            domain=['1955', '2000'],\n+            domain=[1955, 2000],\n             range=['#e6959c', '#911a24']\n         )\n     )\n ).interactive()\n \n-chart\n+(line + points)\n", "issue": "Dots aren't showing up in ranged dot plot\n![Screenshot from 2022-06-30 20-02-14](https://user-images.githubusercontent.com/9993/176815294-a1801b76-ed5a-4f3c-b38f-71850c131a5a.png)\r\n\n", "before_files": [{"content": "\"\"\"\nRanged Dot Plot\n-----------------\nThis example shows a ranged dot plot that uses 'layer' to convey changing life expectancy for the five most populous countries (between 1955 and 2000).\n\"\"\"\n# category: other charts\nimport altair as alt\nfrom vega_datasets import data\n\nsource = data.countries.url\n\nchart = alt.layer(\n    data=source\n).transform_filter(\n    filter={\"field\": 'country',\n            \"oneOf\": [\"China\", \"India\", \"United States\", \"Indonesia\", \"Brazil\"]}\n).transform_filter(\n    filter={'field': 'year',\n            \"oneOf\": [1955, 2000]}\n)\n\nchart += alt.Chart().mark_line(color='#db646f').encode(\n    x='life_expect:Q',\n    y='country:N',\n    detail='country:N'\n)\n# Add points for life expectancy in 1955 & 2000\nchart += alt.Chart().mark_point(\n    size=100,\n    opacity=1,\n    filled=True\n).encode(\n    x='life_expect:Q',\n    y='country:N',\n    color=alt.Color('year:O',\n        scale=alt.Scale(\n            domain=['1955', '2000'],\n            range=['#e6959c', '#911a24']\n        )\n    )\n).interactive()\n\nchart\n", "path": "altair/examples/ranged_dot_plot.py"}], "after_files": [{"content": "\"\"\"\nRanged Dot Plot\n---------------\nThis example shows a ranged dot plot to convey changing life expectancy for the five most populous countries (between 1955 and 2000).\n\"\"\"\n# category: other charts\nimport altair as alt\nfrom vega_datasets import data\n\nsource = data.countries.url\n\nchart = alt.Chart(\n    data=source\n).transform_filter(\n    filter={\"field\": 'country',\n            \"oneOf\": [\"China\", \"India\", \"United States\", \"Indonesia\", \"Brazil\"]}\n).transform_filter(\n    filter={'field': 'year',\n            \"oneOf\": [1955, 2000]}\n)\n\nline = chart.mark_line(color='#db646f').encode(\n    x='life_expect:Q',\n    y='country:N',\n    detail='country:N'\n)\n# Add points for life expectancy in 1955 & 2000\npoints = chart.mark_point(\n    size=100,\n    opacity=1,\n    filled=True\n).encode(\n    x='life_expect:Q',\n    y='country:N',\n    color=alt.Color('year:O',\n        scale=alt.Scale(\n            domain=[1955, 2000],\n            range=['#e6959c', '#911a24']\n        )\n    )\n).interactive()\n\n(line + points)\n", "path": "altair/examples/ranged_dot_plot.py"}]}