Quality of life fixes for easier hacking (#982)

Author: Kontinuation

common/src/main/java/org/apache/comet/NativeBase.java

@@ -81,7 +81,7 @@ static synchronized void load() {
 
     // Try to load Comet library from the java.library.path.
     try {
-      System.loadLibrary(libraryToLoad);
+      System.loadLibrary(NATIVE_LIB_NAME);
       loaded = true;
     } catch (UnsatisfiedLinkError ex) {
       // Doesn't exist, so proceed to loading bundled library.

native/core/src/jvm_bridge/mod.rs

@@ -339,7 +339,7 @@ fn get_throwable_message(
     throwable: &JThrowable,
 ) -> CometResult<String> {
     unsafe {
-        let message = env
+        let message: JString = env
             .call_method_unchecked(
                 throwable,
                 jvm_classes.throwable_get_message_method,
@@ -348,7 +348,11 @@ fn get_throwable_message(
             )?
             .l()?
             .into();
-        let message_str = env.get_string(&message)?.into();
+        let message_str = if !message.is_null() {
+            env.get_string(&message)?.into()
+        } else {
+            String::from("null")
+        };
 
         let cause: JThrowable = env
             .call_method_unchecked(

spark/src/test/scala/org/apache/comet/CometNativeSuite.scala

@@ -0,0 +1,51 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.comet
+
+import org.apache.spark.SparkException
+import org.apache.spark.sql.CometTestBase
+import org.apache.spark.sql.catalyst.expressions.PrettyAttribute
+import org.apache.spark.sql.comet.{CometExec, CometExecUtils}
+import org.apache.spark.sql.types.LongType
+import org.apache.spark.sql.vectorized.ColumnarBatch
+
+class CometNativeSuite extends CometTestBase {
+  test("test handling NPE thrown by JVM") {
+    val rdd = spark.range(0, 1).rdd.map { value =>
+      val limitOp =
+        CometExecUtils.getLimitNativePlan(Seq(PrettyAttribute("test", LongType)), 100).get
+      val cometIter = CometExec.getCometIterator(
+        Seq(new Iterator[ColumnarBatch] {
+          override def hasNext: Boolean = true
+          override def next(): ColumnarBatch = throw new NullPointerException()
+        }),
+        1,
+        limitOp)
+      cometIter.next()
+      cometIter.close()
+      value
+    }
+
+    val exception = intercept[SparkException] {
+      rdd.collect()
+    }
+    assert(exception.getMessage contains "java.lang.NullPointerException")
+  }
+}