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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.


import liquibase.util.SmartMap;
import liquibase.util.StringUtil;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Constructor;
import java.nio.charset.Charset;
import java.util.*;
/**
 * This scope object is used to hold configuration and other parameters within a call without needing complex method signatures.
 * It also allows new parameters to be added by extensions without affecting standard method signatures.
 * Scope objects can be created in a hierarchical manner with the {@link #child(Map, ScopedRunner)} or {@link #child(String, Object, ScopedRunner)} methods.
 * Values set in parent scopes are visible in child scopes, but values in child scopes are not visible to parent scopes.
 * Values with the same key in different scopes "mask" each other with the value furthest down the scope chain being returned.
 */
public class Scope {
    /**
     * Enumeration containing standard attributes. Normally use methods like convenience {@link #getResourceAccessor()} or {@link #getDatabase()}
     */
    public enum Attr {
        logService,
        ui,
        resourceAccessor,
        classLoader,
        database,
        quotingStrategy,
        changeLogHistoryService,
        lockService,
        executeMode,
        lineSeparator,
        serviceLocator,