Grails3.3.9 as JSON variable dont GC

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Defines a utils class, Used to convert domain instances into Map,
The following code：
`public static def domainFormat(domain) {
def result = domain as JSON
try{
return (Map)JSON.parse(result.toString())
}catch(e){
e.printStackTrace()
}
}`
However, in the production environment variables are not recycled（GC）,This often results in full memory and FULL CPU，
Grab the stack memory of the production environment and analyze all points to this public method

### Task List

- [ ] Steps to reproduce provided
- [ ] Stacktrace (if present) provided
- [ ] Example that reproduces the problem uploaded to Github
- [ ] Full description of the issue provided (see below)

### Steps to Reproduce

1. TODO
defined utils class:

`public static def domainFormat(domain) {
def result = domain as JSON
try{
return (Map)JSON.parse(result.toString())
}catch(e){
e.printStackTrace()
}
}`

2. TODO
def book = Book.get(1)
Map map = domainFormat(book )
map.tttt = "demo"
render map as JSON
3. TODO

### Expected Behaviour

Tell us what should happen

### Actual Behaviour

Tell us what happens instead

### Environment Information

- **Operating System**: win10
- **Grails Version:** 3.3.9
- **JDK Version:** 1.8
- **Container Version (If Applicable):** TODO

### Example Application

- TODO: link to github repository with example that reproduces the issue

Start with the domainFormat utility and the Book.get(1), map modification, and render map as JSON sequence given in the report. Establish a reproducible example and capture the expected and actual memory or GC behavior; the issue is not ready for implementation until those details and an example application are provided.

Written by the indexing model from the issue text.