### 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
var indices = List.of(indexName1, indexName2);
        var alias = "test-alias";
        int docsCount = randomIntBetween(50, 100);
        int[] countValuesGreaterThanFifty = new int[indices.size()];
        for (int i = 0; i < indices.size(); i++) {
            String indexName = indices.get(i);
            createNestedMappingIndex(indexName);
            countValuesGreaterThanFifty[i] = indexDocsIntoNestedMappingIndex(indexName, docsCount);
        }
        createAlias(indices, alias);
        var indexToTest = randomIntBetween(0, indices.size() - 1);
        var indexNameToTest = indices.get(indexToTest);
        
        assertNoNestedDocuments("from " + indexNameToTest, docsCount, 0L, 100L);
        
        assertNoNestedDocuments("from " + indexNameToTest + " | where data >= 50", countValuesGreaterThanFifty[indexToTest], 50L, 100L);
        
        assertNoNestedDocuments("from " + alias, docsCount * 2, 0L, 100L);
        
        assertNoNestedDocuments("from " + alias + " | where data >= 50", Arrays.stream(countValuesGreaterThanFifty).sum(), 50L, 100L);
    }
    private void createNestedMappingIndex(String indexName) throws IOException {
        XContentBuilder builder = JsonXContent.contentBuilder();
        builder.startObject();
        {
            builder.startObject("properties");
            {
                builder.startObject("nested");
                {
                    builder.field("type", "nested");