Handle missing default VMInstall when querying JVM system-packages

build/org.eclipse.pde.build/src/org/eclipse/pde/internal/build/site/PDEState.java

@@ -532,14 +532,18 @@
 				if (javaPackages == null) {
 					String profileSystemPackages = preJava9ProfileProperties.getProperty(Constants.FRAMEWORK_SYSTEMPACKAGES, ""); //$NON-NLS-1$
 					if (profileSystemPackages.isBlank()) {
-						return null;
+						return List.of();
 					}
 					javaPackages = COMMA.splitAsStream(profileSystemPackages).filter(p -> p.startsWith("java.")).toList(); //$NON-NLS-1$
 				}
 				IVMInstall targetVM = JavaRuntime.getDefaultVMInstall(); // Set by the Target-Definition if specified there
+				if (targetVM == null) {
+					LOGGER.warn("No default JRE installation selected"); //$NON-NLS-1$
+					return List.of();
+				}
 				Collection<String> targetVMSystemPackages = querySystemPackages(targetVM, null);
 				if (targetVMSystemPackages == null) {
-					return null;
+					return List.of();
 				}
 				Stream<String> targetVMNonJavaPackages = targetVMSystemPackages.stream().filter(p -> !p.startsWith("java.")); //$NON-NLS-1$
 
@@ -666,17 +670,17 @@
 		String release = environment != null ? environment.getProfileProperties().getProperty(JavaCore.COMPILER_COMPLIANCE) : null;
 		try {
 			Collection<String> packages = new TreeSet<>();
 			String jrtPath = "lib/" + org.eclipse.jdt.internal.compiler.util.JRTUtil.JRT_FS_JAR; //$NON-NLS-1$
 			String path = new File(vm.getInstallLocation(), jrtPath).toString(); // $NON-NLS-1$
 			var jrt = org.eclipse.jdt.internal.core.builder.ClasspathLocation.forJrtSystem(path, null, null, release);
 			for (String moduleName : jrt.getModuleNames(null)) {
 				var module = jrt.getModule(moduleName);
 				if (module == null) {
 					continue;
 				}
 				for (var packageExport : module.exports()) {
 					if (!packageExport.isQualified()) {
 						packages.add(new String(packageExport.name()));
 					}
 				}
 			}