### Elasticsearch Version

8.11.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

MacOS

### Problem Description

When sending a ESQL query with the `enrich` command that involves a policy that does not existing a `NullPointerException` is thrown and shown as error messages to the user:

Query:
```
row a  = 1| enrich missing-policy
```

Returns:
```
null_pointer_exception - Cannot invoke "org.elasticsearch.xpack.core.enrich.EnrichPolicy.getMatchField()" because "policy" is null
```

### Steps to Reproduce

See above.

### Logs (if relevant)

_No response_
x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/AnalyzerTests.java
| rename emp_no as e
            | keep first_name, e
            """, "first_name", "e");
    }
    public void testChainedRename() {
        assertProjection("""
            from test
            | rename emp_no as r1, r1 as r2, r2 as r3
            | keep first_name, r3
            """, "first_name", "r3");
    }
    public void testChainedRenameReuse() {
        assertProjection("""
            from test
            | rename emp_no as r1, r1 as r2, r2 as r3, first_name as r1
            | keep r1, r3
            """, "r1", "r3");
    }
    public void testRenameBackAndForth() {
        assertProjection("""
            from test
            | rename emp_no as r1, r1 as emp_no
            | keep emp_no
            """, "emp_no");
    }
    public void testRenameReuseAlias() {
        assertProjection("""
            from test
            | rename emp_no as e, first_name as e
            """, "_meta_field", "e", "gender", "job", "job.raw", "languages", "last_name", "long_noidx", "salary");