### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

all

### Problem Description

Do this

### Steps to Reproduce

```
rm /tmp/evil
for a in {0..9}; do
   for b in {0..9}; do
      echo '{"index": {}}' >> /tmp/evil
      echo '{"a": '$a', "b": '$b'}' >> /tmp/evil
   done
done
echo >> /tmp/evil

curl -uelastic:password -XDELETE localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPUT localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_bulk --data-binary @/tmp/evil
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_forcemerge?max_num_segments=1
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_refresh

curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/_esql?pretty -d'{
   "query": "FROM test | STATS MAX(a) BY a, b | KEEP a"
}'
```

### Logs (if relevant)

_No response_
x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/CsvTestUtils.java
throw new IllegalArgumentException("Null type is not allowed in the test data; found " + entries[i]);
                            }
                            columns[i] = new CsvColumn(name, type, BlockUtils.wrapperFor(ElementType.fromJava(type.clazz()), 8));
                        }
                    }
                    
                    else {
                        if (entries.length != columns.length) {
                            throw new IllegalArgumentException(
                                format(
                                    "Error line [{}]: Incorrect number of entries; expected [{}] but found [{}]",
                                    lineNumber,
                                    columns.length,
                                    entries.length
                                )
                            );
                        }
                        for (int i = 0; i < entries.length; i++) {
                            var entry = entries[i];
                            try {
                                columns[i].append(entry);
                            } catch (Exception e) {
                                throw new IllegalArgumentException(
                                    format("Error line [{}]: Cannot parse entry [{}] with value [{}]", lineNumber, i + 1, entry),
                                    e
                                );
                            }
                        }
                    }
                }