### Description

`from employees | eval x = 1 | keep x` results in 

```
Caused by: java.lang.NullPointerException: Cannot invoke "java.lang.Integer.intValue()" because the return value of "org.elasticsearch.xpack.esql.planner.Layout.getChannel(org.elasticsearch.xpack.ql.expression.NameId)" is null
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.alignPageToAttributes(LocalExecutionPlanner.java:281)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planExchangeSink(LocalExecutionPlanner.java:305)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:199)
        at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.plan(LocalExecutionPlanner.java:146)
        at org.elasticsearch.xpack.esql.plugin.ComputeService.runCompute(ComputeService.java:246)
        at org.elasticsearch.xpack.esql.plugin.ComputeService$DataNodeRequestHandler.lambda$messageReceived$5(ComputeService.java:415)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.action.ActionListener$2.onResponse(ActionListener.java:177)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.action.ActionListener.completeWith(ActionListener.java:305)
        at org.elasticsearch.xpack.esql.plugin.ComputeService.lambda$acquireSearchContexts$13(ComputeService.java:280)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.index.shard.IndexShard.ensureShardSearchActive(IndexShard.java:3911)
        at org.elasticsearch.xpack.esql.plugin.ComputeService.acquireSearchContexts(ComputeService.java:278)
        at org.elasticsearch.xpack.esql.plugin.ComputeService$DataNodeRequestHandler.messageReceived(ComputeService.java:413)
        at org.elasticsearch.xpack.esql.plugin.ComputeService$DataNodeRequestHandler.messageReceived(ComputeService.java:405)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:74)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.transport.TransportService$6.doRun(TransportService.java:1023)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:983)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:26)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:33)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:983)
        at org.elasticsearch.server@8.10.0-SNAPSHOT/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:26)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
        at java.base/java.lang.Thread.run(Thread.java:1623)
```
x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/EsqlActionIT.java
testFromStatsGroupingAvgImpl("from test | stats avg(count) by data", "data", "avg(count)");
    }
    public void testFromStatsGroupingAvgWithAliases() {
        testFromStatsGroupingAvgImpl("from test | eval g = data | stats f = avg(count) by g", "g", "f");
    }
    private void testFromStatsGroupingAvgImpl(String command, String expectedGroupName, String expectedFieldName) {
        EsqlQueryResponse results = run(command);
        logger.info(results);
        Assert.assertEquals(2, results.columns().size());
        
        ColumnInfo valuesColumn = results.columns().get(0);
        assertEquals(expectedFieldName, valuesColumn.name());
        assertEquals("double", valuesColumn.type());
        ColumnInfo groupColumn = results.columns().get(1);
        assertEquals(expectedGroupName, groupColumn.name());
        assertEquals("long", groupColumn.type());
        
        List<List<Object>> valueValues = results.values();
        assertEquals(2, valueValues.size());
        
        if ((long) valueValues.get(0).get(1) == 1L) {
            assertEquals(42.0, (double) valueValues.get(0).get(0), 0.0);
            assertEquals(2L, (long) valueValues.get(1).get(1));
            assertEquals(44.0, (double) valueValues.get(1).get(0), 0.0);
        } else if ((long) valueValues.get(0).get(1) == 2L) {
            assertEquals(42.0, (double) valueValues.get(1).get(0), 0.0);
            assertEquals(1L, (long) valueValues.get(1).get(1));
            assertEquals(44.0, (double) valueValues.get(0).get(0), 0.0);
        } else {
            fail("Unexpected group value: " + valueValues.get(0).get(0));