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## Environment
**Liquibase Version**: 4.0.0

## Description
I am getting an NPE when I create a new FileSystemResourceAccessor(rootPath), with the following stack trace:

```
java.lang.NullPointerException
        at liquibase.Scope.getLog(Scope.java:278)
        at liquibase.resource.FileSystemResourceAccessor.addRootPath(FileSystemResourceAccessor.java:54)
        at liquibase.resource.FileSystemResourceAccessor.<init>(FileSystemResourceAccessor.java:36)
```

Looking at the Liquibase code, I see that SmartMap#get defines its result as a nullable, however, the Scope class does not check for null in this and other places.

## Steps To Reproduce
I'm running tests in my project, using liquibase-core:
Created this issue for tracking purposes, where you can also find the full stack trace: https://github.com/Treehopper/liquibase-lsp/issues/17

## Additional Context
In my project, I have to run scripts asynchronously. This, and the fact that the problem only occurs occasionally hints at a race-condition.


serviceLocator = possibleLocator;
                }
            }
            rootScope.values.put(Attr.serviceLocator.name(), serviceLocator);
        }
        return scopeManager.getCurrentScope();
    }
    public static void setScopeManager(ScopeManager scopeManager)  {
        Scope currentScope = getCurrentScope();
        if (currentScope == null) {
            currentScope = new Scope();
        }
        try {
            currentScope = scopeManager.init(currentScope);
        } catch (Exception e) {
            Scope.getCurrentScope().getLog(Scope.class).warning(e.getMessage(), e);
        }
        scopeManager.setCurrentScope(currentScope);
        Scope.scopeManager = scopeManager;
    }
    /**
     * Creates a new "root" scope.
     * Defaults resourceAccessor to {@link ClassLoaderResourceAccessor}.
     * Defaults serviceLocator to {@link StandardServiceLocator}
     */
    private Scope() {
    }
    protected Scope(Scope parent, Map<String, Object> scopeValues) {
        this.parent = parent;
        if (scopeValues != null) {