fixed potential null pointer exception
diff --git a/plugins/org.eclipse.epp.installer.core/src/org/eclipse/epp/installer/internal/core/eclipse/EclipseProductType.java b/plugins/org.eclipse.epp.installer.core/src/org/eclipse/epp/installer/internal/core/eclipse/EclipseProductType.java
index b87aa80..9e67b39 100644
--- a/plugins/org.eclipse.epp.installer.core/src/org/eclipse/epp/installer/internal/core/eclipse/EclipseProductType.java
+++ b/plugins/org.eclipse.epp.installer.core/src/org/eclipse/epp/installer/internal/core/eclipse/EclipseProductType.java
@@ -464,9 +464,9 @@
 	static EclipseVersion readVersionFromPluginDir(File eclipseDir, String pluginDirPrefix) {
 		File pluginsDir = new File(eclipseDir, PLUGINS_DIR_NAME);
 		String[] names = pluginsDir.list();
-		Arrays.sort(names);
 		if (names == null)
 			return null;
+		Arrays.sort(names);
 		for (int i = 0; i < names.length; i++) {
 			String eachName = names[i];
 			if (eachName.startsWith(pluginDirPrefix)) {