Fix NullPointerException in cache pre-warming

- Add null/empty validation for className in ContainerCoordinator.preWarmCriticalCaches()
- Add null checks in AsmCoreUtils for getClassInfo(), findMethods(), findConstructors(), findFields()
- Prevent ConcurrentHashMap.putVal() failures when className is null or empty
- Add logging for unavailable classes during pre-warming

Fixes test failure: FrameworkIntegrationTest.testEventHealthCheckIntegration

Author: yasmramos

warmup-core/src/main/java/io/warmup/framework/asm/AsmCoreUtils.java

@@ -209,13 +209,23 @@ public AsmFieldInfo(String name, String descriptor, String type,
      * ✅ OBTIENE INFORMACIÓN COMPLETA DE UNA CLASE USANDO ASM
      */
     public static AsmClassInfo getClassInfo(String className) {
+        // ✅ FIX: Verificar que className no sea null o vacío antes de procesar
+        if (className == null || className.isEmpty()) {
+            log.log(Level.WARNING, "Attempted to get class info for null or empty class name");
+            return null;
+        }
         return asmClassInfoCache.computeIfAbsent(className, AsmCoreUtils::analyzeClassWithASM);
     }
 
     /**
      * ✅ ENCUENTRA MÉTODOS ESPECÍFICOS EN UNA CLASE
      */
     public static List<AsmMethodInfo> findMethods(String className, String methodName) {
+        // ✅ FIX: Verificar que className no sea null o vacío
+        if (className == null || className.isEmpty()) {
+            log.log(Level.WARNING, "Attempted to find methods in null or empty class name");
+            return new ArrayList<>();
+        }
         String cacheKey = className + "." + methodName;
         return asmMethodCache.computeIfAbsent(cacheKey, k -> {
             AsmClassInfo classInfo = getClassInfo(className);
@@ -250,6 +260,11 @@ public static AsmMethodInfo findMethodExact(String className, String methodName,
      * ✅ ENCUENTRA CONSTRUCTORES ESPECÍFICOS
      */
     public static List<AsmConstructorInfo> findConstructors(String className) {
+        // ✅ FIX: Verificar que className no sea null o vacío
+        if (className == null || className.isEmpty()) {
+            log.log(Level.WARNING, "Attempted to find constructors in null or empty class name");
+            return new ArrayList<>();
+        }
         String cacheKey = className + ".<init>";
         return asmConstructorCache.computeIfAbsent(cacheKey, k -> {
             AsmClassInfo classInfo = getClassInfo(className);
@@ -277,6 +292,11 @@ public static AsmConstructorInfo findConstructorExact(String className, String..
      * ✅ ENCUENTRA CAMPOS ESPECÍFICOS
      */
     public static List<AsmFieldInfo> findFields(String className) {
+        // ✅ FIX: Verificar que className no sea null o vacío
+        if (className == null || className.isEmpty()) {
+            log.log(Level.WARNING, "Attempted to find fields in null or empty class name");
+            return new ArrayList<>();
+        }
         String cacheKey = className + ".<field>";
         return asmFieldCache.computeIfAbsent(cacheKey, k -> {
             AsmClassInfo classInfo = getClassInfo(className);

warmup-core/src/main/java/io/warmup/framework/core/optimized/ContainerCoordinator.java

@@ -221,20 +221,28 @@ private void preWarmCriticalCaches(ASMCacheManager cacheManager) {
 
             for (String className : criticalClasses) {
                 try {
+                    // ✅ FIX: Verificar que className no sea null antes de procesar
+                    if (className == null || className.isEmpty()) {
+                        log.log(Level.FINE, "Skipping null or empty class name in pre-warm");
+                        continue;
+                    }
+                    
                     // Pre-cargar información de clase en cache
                     // Solo registrar información básica de clase, no bytecode directamente
                     io.warmup.framework.asm.AsmCoreUtils.AsmClassInfo classInfo = 
                         io.warmup.framework.asm.AsmCoreUtils.getClassInfo(className);
                     if (classInfo != null) {
                         // Marcar la clase como pre-cargada para futura optimización
                         log.log(Level.FINE, "Pre-warmed class info: " + className);
+                    } else {
+                        log.log(Level.FINE, "Class not available for pre-warming: " + className);
                     }
                 } catch (Exception e) {
                     log.log(Level.FINE, "Could not pre-warm class: " + className, e);
                 }
             }
 
-            log.log(Level.INFO, "Pre-warmed {0} critical classes in ASM cache", criticalClasses.length);
+            log.log(Level.INFO, "Pre-warm cache operation completed for critical classes");
 
         } catch (Exception e) {
             log.log(Level.WARNING, "Error during cache pre-warming", e);