From 484929d1f8e5fbcded26cc5466757e2805e3ac76 Mon Sep 17 00:00:00 2001
From: Ulrich Kramer <u.kramer@sap.com>
Date: Tue, 17 Oct 2023 17:44:15 +0200
Subject: [PATCH] Add Schemas.getExistingSubSchema to avoid
 NullPointerException

---
 .../org/apache/calcite/schema/Schemas.java    | 22 +++++++++++--------
 .../apache/calcite/util/BuiltInMethod.java    |  1 +
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/core/src/main/java/org/apache/calcite/schema/Schemas.java b/core/src/main/java/org/apache/calcite/schema/Schemas.java
index c007701bd255..4e3343511fc3 100644
--- a/core/src/main/java/org/apache/calcite/schema/Schemas.java
+++ b/core/src/main/java/org/apache/calcite/schema/Schemas.java
@@ -51,13 +51,7 @@
 
 import java.lang.reflect.Type;
 import java.sql.Connection;
-import java.util.AbstractList;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.Iterator;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 import static org.apache.calcite.jdbc.CalciteSchema.LatticeEntry;
 
@@ -125,9 +119,8 @@ public static Expression subSchemaExpression(SchemaPlus schema, String name,
     // (Type) schemaExpression.getSubSchema("name")
     final Expression schemaExpression = expression(schema);
     Expression call =
-        Expressions.call(
+        Expressions.call(BuiltInMethod.SCHEMAS_GET_EXISTING_SUB_SCHEMA.method,
             schemaExpression,
-            BuiltInMethod.SCHEMA_GET_SUB_SCHEMA.method,
             Expressions.constant(name));
     //CHECKSTYLE: IGNORE 2
     //noinspection unchecked
@@ -137,6 +130,15 @@ public static Expression subSchemaExpression(SchemaPlus schema, String name,
     return call;
   }
 
+  public static SchemaPlus getExistingSubSchema(SchemaPlus schema, String name){
+    SchemaPlus subSchema = schema.getSubSchema(name);
+    if ( subSchema == null ) {
+      throw new NoSuchElementException("Sub schema " +  name + " not found in " + schema.toString());
+    }
+    return subSchema;
+  }
+
+
   /** Converts a schema expression to a given type by calling the
    * {@link SchemaPlus#unwrap(Class)} method. */
   public static Expression unwrap(Expression call, Class type) {
@@ -648,4 +650,6 @@ private static class PathImpl
       return Pair.right(pairs);
     }
   }
+
+
 }
diff --git a/core/src/main/java/org/apache/calcite/util/BuiltInMethod.java b/core/src/main/java/org/apache/calcite/util/BuiltInMethod.java
index 8865e1024964..b4d9edbf9bc1 100644
--- a/core/src/main/java/org/apache/calcite/util/BuiltInMethod.java
+++ b/core/src/main/java/org/apache/calcite/util/BuiltInMethod.java
@@ -161,6 +161,7 @@ public enum BuiltInMethod {
   SCHEMA_PLUS_ADD_TABLE(SchemaPlus.class, "add", String.class, Table.class),
   SCHEMA_PLUS_REMOVE_TABLE(SchemaPlus.class, "removeTable", String.class),
   SCHEMA_PLUS_UNWRAP(SchemaPlus.class, "unwrap", Class.class),
+  SCHEMAS_GET_EXISTING_SUB_SCHEMA(Schemas.class, "getExistingSubSchema", SchemaPlus.class, String.class),
   SCHEMAS_ENUMERABLE_SCANNABLE(Schemas.class, "enumerable",
       ScannableTable.class, DataContext.class),
   SCHEMAS_ENUMERABLE_FILTERABLE(Schemas.class, "enumerable",