Can't turn ON the auto-closing feature

My notebook sometimes cannot auto complete bracket and quotes (and what makes the situation more complicated, it sometimes works). I search this issue on google and found a method to turn OFF autoCloseBracket:
```
from notebook.services.config import ConfigManager
c = ConfigManager()
c.update('notebook', {"CodeCell": {"cm_config": {"autoCloseBrackets": False}}})
```
So, I changed the argument to "True", but still it does not work.

I also directly opened notebook.json, where I found the code below.
```
{
"CodeCell": {
"cm_config": {
"autoCloseBrackets": true
}
}
}
```
Although it seems that the auto-closing feature in my jupyter notebook is successfully turned on,
it still does not work in fact.

MacOS 10.14
jupyter notebook 4.4.0

I appreciate all your help, thank you.

Start by reproducing the auto-closing behavior in Jupyter Notebook 4.4.0 on macOS, then inspect the ConfigManager settings for notebook.json and the CodeCell cm_config entry. Confirm whether setting autoCloseBrackets to true changes the editor behavior and document the result.

Written by the indexing model from the issue text.