[MINOR] Fix a potential NPE and some finer points of hudi cli

hudi-cli/src/main/java/org/apache/hudi/cli/commands/MetadataCommand.java

@@ -364,7 +364,7 @@ private HoodieWriteConfig getWriteConfig() {
 
   private void initJavaSparkContext(Option<String> userDefinedMaster) {
     if (jsc == null) {
-      jsc = SparkUtil.initJavaSparkConf(SparkUtil.getDefaultConf("HoodieCLI", userDefinedMaster));
+      jsc = SparkUtil.initJavaSparkContext(SparkUtil.getDefaultConf("HoodieCLI", userDefinedMaster));
     }
   }
 }

hudi-cli/src/main/java/org/apache/hudi/cli/commands/SparkMain.java

@@ -95,7 +95,7 @@ public static void main(String[] args) throws Exception {
     LOG.info("Invoking SparkMain: " + commandString);
     final SparkCommand cmd = SparkCommand.valueOf(commandString);
 
-    JavaSparkContext jsc = SparkUtil.initJavaSparkConf("hoodie-cli-" + commandString,
+    JavaSparkContext jsc = SparkUtil.initJavaSparkContext("hoodie-cli-" + commandString,
         Option.of(args[1]), Option.of(args[2]));
 
     int returnCode = 0;

hudi-cli/src/main/java/org/apache/hudi/cli/commands/UpgradeOrDowngradeCommand.java

@@ -56,7 +56,7 @@ public String upgradeHoodieTable(
     if (exitCode != 0) {
       return String.format("Failed: Could not Upgrade/Downgrade Hoodie table to \"%s\".", toVersion);
     }
-    return String.format("Hoodie table upgraded/downgraded to ", toVersion);
+    return String.format("Hoodie table upgraded/downgraded to %s", toVersion);
   }
 
   @CliCommand(value = "downgrade table", help = "Downgrades a table")
@@ -78,6 +78,6 @@ public String downgradeHoodieTable(
     if (exitCode != 0) {
       return String.format("Failed: Could not Upgrade/Downgrade Hoodie table to \"%s\".", toVersion);
     }
-    return String.format("Hoodie table upgraded/downgraded to ", toVersion);
+    return String.format("Hoodie table upgraded/downgraded to %s", toVersion);
   }
 }

hudi-cli/src/main/java/org/apache/hudi/cli/utils/SparkUtil.java

@@ -32,8 +32,8 @@
 
 import java.io.File;
 import java.net.URISyntaxException;
+import java.util.Arrays;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Properties;
 
 /**
@@ -56,9 +56,12 @@ public static SparkLauncher initLauncher(String propertiesFile) throws URISyntax
     if (!StringUtils.isNullOrEmpty(propertiesFile)) {
       sparkLauncher.setPropertiesFile(propertiesFile);
     }
+
     File libDirectory = new File(new File(currentJar).getParent(), "lib");
-    for (String library : Objects.requireNonNull(libDirectory.list())) {
-      sparkLauncher.addJar(new File(libDirectory, library).getAbsolutePath());
+    // This lib directory may be not required, such as providing libraries through a bundle jar
+    if (libDirectory.exists()) {
+      Arrays.stream(libDirectory.list()).forEach(library ->
+              sparkLauncher.addJar(new File(libDirectory, library).getAbsolutePath()));
     }
     return sparkLauncher;
   }
@@ -99,20 +102,20 @@ public static SparkConf getDefaultConf(final String appName, final Option<String
     return sparkConf;
   }
 
-  public static JavaSparkContext initJavaSparkConf(String name) {
-    return initJavaSparkConf(name, Option.empty(), Option.empty());
+  public static JavaSparkContext initJavaSparkContext(String name) {
+    return initJavaSparkContext(name, Option.empty(), Option.empty());
   }
 
-  public static JavaSparkContext initJavaSparkConf(String name, Option<String> master, Option<String> executorMemory) {
+  public static JavaSparkContext initJavaSparkContext(String name, Option<String> master, Option<String> executorMemory) {
     SparkConf sparkConf = getDefaultConf(name, master);
     if (executorMemory.isPresent()) {
       sparkConf.set(HoodieCliSparkConfig.CLI_EXECUTOR_MEMORY, executorMemory.get());
     }
 
-    return initJavaSparkConf(sparkConf);
+    return initJavaSparkContext(sparkConf);
   }
 
-  public static JavaSparkContext initJavaSparkConf(SparkConf sparkConf) {
+  public static JavaSparkContext initJavaSparkContext(SparkConf sparkConf) {
     SparkRDDWriteClient.registerClasses(sparkConf);
     JavaSparkContext jsc = new JavaSparkContext(sparkConf);
     jsc.hadoopConfiguration().setBoolean(HoodieCliSparkConfig.CLI_PARQUET_ENABLE_SUMMARY_METADATA, false);

hudi-cli/src/test/java/org/apache/hudi/cli/testutils/SparkUtilTest.java

@@ -22,11 +22,22 @@
 import org.apache.hudi.cli.utils.SparkUtil;
 import org.apache.spark.SparkConf;
 
+import org.apache.spark.launcher.SparkLauncher;
 import org.junit.jupiter.api.Test;
 
+import java.net.URISyntaxException;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 public class SparkUtilTest {
+
+  @Test
+  public void testInitSparkLauncher() throws URISyntaxException {
+    SparkLauncher sparkLauncher = SparkUtil.initLauncher(null);
+    assertNotNull(sparkLauncher);
+  }
+
   @Test
   public void testGetDefaultSparkConf() {
     SparkConf sparkConf = SparkUtil.getDefaultConf("test-spark-app", Option.of(""));