The Babel parser can supply null for column strategies

Signed-off-by: Mihai Budiu <mbudiu@feldera.com>

Author: mihaibudiu

core/src/main/java/org/apache/calcite/sql/ddl/SqlColumnDeclaration.java

@@ -58,6 +58,7 @@ public class SqlColumnDeclaration extends SqlCall {
   public final SqlIdentifier name;
   public final SqlDataTypeSpec dataType;
   public final @Nullable SqlNode expression;
+  // The Babel parser can supply null for the strategy
   public final @Nullable ColumnStrategy strategy;
 
   /** Creates a SqlColumnDeclaration; use {@link SqlDdlNodes#column}. */

server/src/main/java/org/apache/calcite/server/ServerDdlExecutor.java

@@ -519,7 +519,12 @@ public void execute(SqlCreateTable create,
         if (d.strategy != ColumnStrategy.VIRTUAL) {
           storedBuilder.add(d.name.getSimple(), type);
         }
-        b.add(ColumnDef.of(d.expression, type, d.strategy));
+        final ColumnStrategy strategy = d.strategy != null
+            ? d.strategy
+            : type.isNullable()
+                ? ColumnStrategy.NULLABLE
+                : ColumnStrategy.NOT_NULLABLE;
+        b.add(ColumnDef.of(d.expression, type, strategy));
       } else if (c.e instanceof SqlIdentifier) {
         final SqlIdentifier id = (SqlIdentifier) c.e;
         if (queryRowType == null) {