[BUG] NPE with json respone formatter on "SELECT 1"

What is the bug?
NPE with json respone formatter on "SELECT 1"

It works fine with default format

curl -X POST "localhost:9200/_plugins/_sql" -H "Content-Type: application/json" -d'
{
        "query": "select 1"
}'
{
  "schema": [
    {
      "name": "1",
      "type": "integer"
    }
  ],
  "datarows": [
    [
      1
    ]
  ],
  "total": 1,
  "size": 1,
  "status": 200
}%    

How can one reproduce the bug?

 curl -X POST "localhost:9200/_plugins/_sql?format=json&pretty=true" -H "Content-Type: application/json" -d'
{
	"query": "select 1"
}'

{
  "error": {
    "reason": "Invalid SQL query",
    "details": "Cannot invoke \"com.alibaba.druid.sql.ast.statement.SQLTableSource.getAlias()\" because the return value of \"com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock.getFrom()\" is null",
    "type": "NullPointerException"
  },
  "status": 400
}

What is the expected behavior?
Return valid json response

Additional info

Stacktrace

java.lang.NullPointerException: Cannot invoke "com.alibaba.druid.sql.ast.statement.SQLTableSource.getAlias()" because the return value of "com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock.getFrom()" is null
	at org.opensearch.sql.legacy.parser.SqlParser.parseSelect(SqlParser.java:81) ~[legacy-3.0.0.0-SNAPSHOT.jar:?]
	at org.opensearch.sql.legacy.parser.SqlParser.parseSelect(SqlParser.java:68) ~[legacy-3.0.0.0-SNAPSHOT.jar:?]
	at org.opensearch.sql.legacy.query.OpenSearchActionFactory.create(OpenSearchActionFactory.java:120) ~[legacy-3.0.0.0-SNAPSHOT.jar:?]
	at org.opensearch.sql.legacy.plugin.SearchDao.explain(SearchDao.java:48) ~[legacy-3.0.0.0-SNAPSHOT.jar:?]
	at org.opensearch.sql.legacy.plugin.RestSqlAction.explainRequest(RestSqlAction.java:243) [legacy-3.0.0.0-SNAPSHOT.jar:?]
	at org.opensearch.sql.legacy.plugin.RestSqlAction.lambda$prepareRequest$1(RestSqlAction.java:172) [legacy-3.0.0.0-SNAPSHOT.jar:?]
	at org.opensearch.sql.legacy.plugin.RestSQLQueryAction.lambda$prepareRequest$0(RestSQLQueryAction.java:92) [legacy-3.0.0.0-SNAPSHOT.jar:?]

Start at org.opensearch.sql.legacy.parser.SqlParser.parseSelect in SqlParser.java:81, using the reproduced POST request with format=json and the SELECT 1 query. Trace how a query without a FROM source is handled and verify the endpoint returns valid JSON without a NullPointerException.