mzyddd

**Small improve performance** - [Minimizing the usage of instanceof checks ] - [uses a combined isinstance check for both NullAction and NullObservation ]

**Small improve performance** - [Minimizing the usage of instanceof checks ] - [uses a combined isinstance check for both NullAction and NullObservation ]

Lingering browser processes

4

## Describe your question I run the main，options is --port 3000 --workers 1 when I opened a web server ，python process adding two ...  when I closed the web...