### 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
} else { 
                        
                        boolean updated = false;
                        if (reverseAliasing.containsValue(resolved.name())) {
                            for (var li = projections.listIterator(); li.hasNext();) {
                                
                                if (li.next() instanceof Alias a && a.name().equals(resolved.name())) {
                                    reverseAliasing.put(resolved.name(), alias.name());
                                    
                                    li.set((NamedExpression) alias.replaceChildren(a.children()));
                                    updated = true;
                                    break;
                                }
                            }
                        }
                        if (updated == false) {
                            var u = resolved;
                            var previousAliasName = reverseAliasing.get(resolved.name());
                            if (previousAliasName != null) {
                                String message = format(
                                    null,
                                    "Column [{}] renamed to [{}] and is no longer available [{}]",
                                    resolved.name(),
                                    previousAliasName,
                                    alias.sourceText()
                                );
                                u = ua.withUnresolvedMessage(message);
                            }
                            unresolved.add(u);
                        }