Fix parameter validation in ApplicationDescriptorDTO, IsolatedClassLoader, and ServiceRegistryImpl

Issue #81: ApplicationDescriptorDTO permission conversion doesn't validate null fields
- Location: toSecurityConfig() method
- Problem: Created Permission objects without validating DTO fields are non-null
- Fix: Added validation for path, host, actions, and permission names
- Impact: Clear error messages instead of NPE when config has null values

Issue #80: IsolatedClassLoader.create() doesn't validate parameters
- Location: static factory method create()
- Problem: No validation of applicationId, descriptor, or platformSharedLoader
- Fix: Added Objects.requireNonNull() for all three parameters
- Impact: Fails fast with clear message instead of NPE deep in factory method

Issue #79: ServiceRegistryImpl methods don't validate parameters
- Location: getService(), getAllServices(), unregisterService()
- Problem: JavaDoc claimed NPE would be thrown but no validation present
- Fix: Added Objects.requireNonNull() for all parameters
- Impact: Contract fulfilled, clearer error messages

All fixes follow defensive programming pattern:
- Validate early (fail fast)
- Clear error messages indicating which parameter was null
- Consistent with existing validation patterns in codebase

Fixes: #81, #80, #79

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Flossy

jplatform-classloader/src/main/java/org/flossware/jplatform/classloader/IsolatedClassLoader.java

@@ -8,6 +8,7 @@
 import java.io.File;
 import java.net.URI;
 import java.util.Map;
+import java.util.Objects;
 
 /**
  * Platform-specific class loader for isolated application execution.
@@ -43,6 +44,9 @@ private IsolatedClassLoader(String applicationId,
     public static IsolatedClassLoader create(String applicationId,
                                              ApplicationDescriptor descriptor,
                                              ClassLoader platformSharedLoader) {
+        Objects.requireNonNull(applicationId, "applicationId cannot be null");
+        Objects.requireNonNull(descriptor, "descriptor cannot be null");
+        Objects.requireNonNull(platformSharedLoader, "platformSharedLoader cannot be null");
 
         ResourceTrackingListener tracker = new ResourceTrackingListener();
 

jplatform-config/src/main/java/org/flossware/jplatform/config/ApplicationDescriptorDTO.java

@@ -200,18 +200,33 @@ public SecurityConfig toSecurityConfig() {
 
             if (filePermissions != null) {
                 for (FilePermissionDTO fp : filePermissions) {
+                    if (fp.path == null || fp.path.trim().isEmpty()) {
+                        throw new IllegalArgumentException("File permission path cannot be null or empty");
+                    }
+                    if (fp.actions == null || fp.actions.trim().isEmpty()) {
+                        throw new IllegalArgumentException("File permission actions cannot be null or empty");
+                    }
                     builder.addFilePermission(new FilePermission(fp.path, fp.actions));
                 }
             }
 
             if (socketPermissions != null) {
                 for (SocketPermissionDTO sp : socketPermissions) {
+                    if (sp.host == null || sp.host.trim().isEmpty()) {
+                        throw new IllegalArgumentException("Socket permission host cannot be null or empty");
+                    }
+                    if (sp.actions == null || sp.actions.trim().isEmpty()) {
+                        throw new IllegalArgumentException("Socket permission actions cannot be null or empty");
+                    }
                     builder.addSocketPermission(new SocketPermission(sp.host, sp.actions));
                 }
             }
 
             if (runtimePermissions != null) {
                 for (String rp : runtimePermissions) {
+                    if (rp == null || rp.trim().isEmpty()) {
+                        throw new IllegalArgumentException("Runtime permission name cannot be null or empty");
+                    }
                     builder.addRuntimePermission(new RuntimePermission(rp));
                 }
             }

jplatform-messaging/src/main/java/org/flossware/jplatform/messaging/ServiceRegistryImpl.java

@@ -101,6 +101,8 @@ public <T> void registerService(Class<T> serviceInterface, T implementation) {
      */
     @Override
     public <T> Optional<T> getService(Class<T> serviceInterface) {
+        Objects.requireNonNull(serviceInterface, "serviceInterface cannot be null");
+
         List<ServiceEntry> entries = services.get(serviceInterface);
 
         if (entries == null || entries.isEmpty()) {
@@ -125,6 +127,8 @@ public <T> Optional<T> getService(Class<T> serviceInterface) {
      */
     @Override
     public <T> List<T> getAllServices(Class<T> serviceInterface) {
+        Objects.requireNonNull(serviceInterface, "serviceInterface cannot be null");
+
         List<ServiceEntry> entries = services.get(serviceInterface);
 
         if (entries == null || entries.isEmpty()) {
@@ -154,6 +158,9 @@ public <T> List<T> getAllServices(Class<T> serviceInterface) {
      */
     @Override
     public void unregisterService(Class<?> serviceInterface, Object implementation) {
+        Objects.requireNonNull(serviceInterface, "serviceInterface cannot be null");
+        Objects.requireNonNull(implementation, "implementation cannot be null");
+
         List<ServiceEntry> entries = services.get(serviceInterface);
 
         if (entries != null) {