### Elasticsearch Version

main@b6747b48ba0901a530ba51375e3576fdb8df8527

### Installed Plugins

_No response_

### Java Version

openjdk version "17.0.8" 2023-07-18

### OS Version

Ubuntu 23.04

### Problem Description

`row a = 1 | stats max(1) by a` (or some other agg) results in:
```
Caused by: java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:233)
	at java.base/java.util.ImmutableCollections$List12.<init>(ImmutableCollections.java:556)
	at java.base/java.util.List.of(List.java:812)
	at org.elasticsearch.xpack.esql.planner.AbstractPhysicalOperationProviders.aggregatesToFactory(AbstractPhysicalOperationProviders.java:185)
	at org.elasticsearch.xpack.esql.planner.AbstractPhysicalOperationProviders.groupingPhysicalOperation(AbstractPhysicalOperationProviders.java:133)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planAggregation(LocalExecutionPlanner.java:207)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:158)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planAggregation(LocalExecutionPlanner.java:207)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:158)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planLimit(LocalExecutionPlanner.java:520)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:176)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planOutput(LocalExecutionPlanner.java:259)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:198)
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:147)
	at org.elasticsearch.xpack.esql.plugin.ComputeService.runCompute(ComputeService.java:204)
	... 147 more
```

@nik9000 's thoughts on this: `I think this is just a kind of special case of "I can't EVAL in STATS". But it's a case the parser accepts.`

### Steps to Reproduce

Run the ESQL query from above.

### Logs (if relevant)

_No response_
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/Verifier.java
b.set(STATS.ordinal());
            } else if (p instanceof Filter) {
                b.set(WHERE.ordinal());
            }
        });
        for (int i = b.nextSetBit(0); i >= 0; i = b.nextSetBit(i + 1)) {
            metrics.inc(FeatureMetric.values()[i]);
        }
    }
    private static Collection<Failure> validateRow(Row row) {
        List<Failure> failures = new ArrayList<>(row.fields().size());
        row.fields().forEach(a -> {
            if (EsqlDataTypes.isRepresentable(a.dataType()) == false) {
                failures.add(fail(a, "cannot use [{}] directly in a row assignment", a.child().sourceText()));
            }
        });
        return failures;
    }
    private static Collection<Failure> validateEval(Eval eval) {
        List<Failure> failures = new ArrayList<>(eval.fields().size());
        eval.fields().forEach(field -> {
            DataType dataType = field.dataType();
            if (EsqlDataTypes.isRepresentable(dataType) == false) {
                failures.add(
                    fail(field, "EVAL does not support type [{}] in expression [{}]", dataType.typeName(), field.child().sourceText())
                );
            }
        });
        return failures;
    }