### 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
from test
            | drop first_name
            | keep *name
            """, "last_name");
    }
    public void testProjectKeepAndDropName() {
        assertProjection("""
            from test
            | drop first_name
            | keep last_name
            """, "last_name");
    }
    public void testProjectDropPattern() {
        assertProjection("""
            from test
            | keep *
            | drop *_name
            """, "_meta_field", "emp_no", "gender", "job", "job.raw", "languages", "long_noidx", "salary");
    }
    public void testProjectDropNoStarPattern() {
        assertProjection("""
            from test
            | drop *_name
            """, "_meta_field", "emp_no", "gender", "job", "job.raw", "languages", "long_noidx", "salary");
    }
    public void testProjectOrderPatternWithRest() {
        assertProjection("""
            from test
            | keep *name, *, emp_no
            """, "first_name", "last_name", "_meta_field", "gender", "job", "job.raw", "languages", "long_noidx", "salary", "emp_no");