### 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/main/java/org/elasticsearch/xpack/esql/analysis/Analyzer.java
import org.elasticsearch.xpack.ql.plan.logical.Project;
import org.elasticsearch.xpack.ql.rule.ParameterizedRule;
import org.elasticsearch.xpack.ql.rule.ParameterizedRuleExecutor;
import org.elasticsearch.xpack.ql.rule.Rule;
import org.elasticsearch.xpack.ql.rule.RuleExecutor;
import org.elasticsearch.xpack.ql.tree.Source;
import org.elasticsearch.xpack.ql.type.DataTypes;
import org.elasticsearch.xpack.ql.type.EsField;
import org.elasticsearch.xpack.ql.type.InvalidMappedField;
import org.elasticsearch.xpack.ql.type.UnsupportedEsField;
import org.elasticsearch.xpack.ql.util.CollectionUtils;
import org.elasticsearch.xpack.ql.util.StringUtils;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
import static java.util.Collections.singletonList;
import static org.elasticsearch.common.logging.LoggerMessageFormat.format;
import static org.elasticsearch.xpack.ql.analyzer.AnalyzerRules.resolveFunction;
import static org.elasticsearch.xpack.ql.type.DataTypes.DATETIME;
import static org.elasticsearch.xpack.ql.type.DataTypes.KEYWORD;
import static org.elasticsearch.xpack.ql.type.DataTypes.NESTED;
public class Analyzer extends ParameterizedRuleExecutor<LogicalPlan, AnalyzerContext> {