### 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
"x",
            "x.y",
            "x.y.z",
            "x.y.z.v",
            "x.y.z.w",
            "some.ambiguous.two",
            "keyword"
        );
    }
    public void testUnsupportedFieldUsedExplicitly2() {
        assertProjectionWithMapping("""
            from test
            | keep keyword, point
            """, "mapping-multi-field-variation.json", "keyword", "point");
    }
    public void testCantFilterAfterDrop() {
        verifyUnsupported("""
            from test
            | stats c = avg(float) by int
            | drop int
            | where int > 0
            """, "Unknown column [int]");
    }
    public void testProjectAggGroupsRefs() {
        assertProjection("""
            from test
            | stats c = count(salary) by last_name
            | eval d = c + 1
            | keep d, last_name
            """, "d", "last_name");