fix(java): fix classloader get npe (apache#1792)

## What does this PR do?

 fix classloader get npe

## Related issues

Closes apache#1763


## Does this PR introduce any user-facing change?

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issue](https://github.com/apache/fury/issues/new/choose) describing the
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- [ ] Does this PR introduce any public API change?
- [ ] Does this PR introduce any binary protocol compatibility change?


## Benchmark

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java/fury-core/src/main/java/org/apache/fury/config/FuryBuilder.java

@@ -321,6 +321,9 @@ public FuryBuilder withScalaOptimizationEnabled(boolean enableScalaOptimization)
   private void finish() {
     if (classLoader == null) {
       classLoader = Thread.currentThread().getContextClassLoader();
+      if (classLoader == null) {
+        classLoader = Fury.class.getClassLoader();
+      }
     }
     if (language != Language.JAVA) {
       stringRefIgnored = false;

java/fury-core/src/main/java/org/apache/fury/pool/FuryPooledObjectFactory.java

@@ -50,7 +50,14 @@ public class FuryPooledObjectFactory {
 
   /** ThreadLocal: ClassLoader. */
   private final ThreadLocal<ClassLoader> classLoaderLocal =
-      ThreadLocal.withInitial(() -> Thread.currentThread().getContextClassLoader());
+      ThreadLocal.withInitial(
+          () -> {
+            ClassLoader loader = Thread.currentThread().getContextClassLoader();
+            if (loader == null) {
+              loader = Fury.class.getClassLoader();
+            }
+            return loader;
+          });
 
   /**
    * Dynamic capacity expansion and contraction The user sets the minimum number of object pools.
@@ -84,6 +91,7 @@ public FuryPooledObjectFactory(
   public ClassLoaderFuryPooled getPooledCache() {
     try {
       ClassLoader classLoader = classLoaderLocal.get();
+      assert classLoader != null;
       ClassLoaderFuryPooled classLoaderFuryPooled =
           classLoaderFuryPooledCache.getIfPresent(classLoader);
       if (classLoaderFuryPooled == null) {