### 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/test/java/org/elasticsearch/xpack/esql/analysis/VerifierTests.java
}
    public void testAggsExpressionsInStatsAggs() {
        assertEquals(
            "1:44: expected an aggregate function or group but got [salary] of type [FieldAttribute]",
            error("from test | eval z = 2 | stats x = avg(z), salary by emp_no")
        );
        assertEquals(
            "1:19: expected an aggregate function or group but got [length(first_name)] of type [Length]",
            error("from test | stats length(first_name), count(1) by first_name")
        );
        assertEquals(
            "1:19: aggregate function's parameters must be an attribute or literal; found [emp_no / 2] of type [Div]",
            error("from test | stats x = avg(emp_no / 2) by emp_no")
        );
        assertEquals(
            "1:25: argument of [avg(first_name)] must be [numeric], found value [first_name] type [keyword]",
            error("from test | stats count(avg(first_name)) by first_name")
        );
        assertEquals(
            "1:19: aggregate function's parameters must be an attribute or literal; found [length(first_name)] of type [Length]",
            error("from test | stats count(length(first_name)) by first_name")
        );
        assertEquals(
            "1:23: expected an aggregate function or group but got [emp_no + avg(emp_no)] of type [Add]",
            error("from test | stats x = emp_no + avg(emp_no) by emp_no")
        );
    }
    public void testDoubleRenamingField() {
        assertEquals(
            "1:44: Column [emp_no] renamed to [r1] and is no longer available [emp_no as r3]",