fix tests after improve PluginDescriptorFinder

pf4j/src/main/java/ro/fortsoft/pf4j/ManifestPluginDescriptorFinder.java

@@ -100,7 +100,9 @@ public class ManifestPluginDescriptorFinder implements PluginDescriptorFinder {
         pluginDescriptor.setPluginClass(clazz);
 
         String version = attributes.getValue("Plugin-Version");
-        pluginDescriptor.setPluginVersion(Version.valueOf(version));
+        if (StringUtils.isNotEmpty(version)) {
+            pluginDescriptor.setPluginVersion(Version.valueOf(version));
+        }
 
         String provider = attributes.getValue("Plugin-Provider");
         pluginDescriptor.setProvider(provider);
@@ -122,6 +124,9 @@ public class ManifestPluginDescriptorFinder implements PluginDescriptorFinder {
         if (StringUtils.isEmpty(pluginDescriptor.getPluginClass())) {
             throw new PluginException("Plugin-Class cannot be empty");
         }
+        if (pluginDescriptor.getVersion() == null) {
+            throw new PluginException("Plugin-Version cannot be empty");
+        }
     }
 
 }

pf4j/src/main/java/ro/fortsoft/pf4j/PropertiesPluginDescriptorFinder.java

@@ -96,7 +96,9 @@ public class PropertiesPluginDescriptorFinder implements PluginDescriptorFinder
         pluginDescriptor.setPluginClass(clazz);
 
         String version = properties.getProperty("plugin.version");
-        pluginDescriptor.setPluginVersion(Version.valueOf(version));
+        if (StringUtils.isNotEmpty(version)) {
+            pluginDescriptor.setPluginVersion(Version.valueOf(version));
+        }
 
         String provider = properties.getProperty("plugin.provider");
         pluginDescriptor.setProvider(provider);
@@ -110,11 +112,13 @@ public class PropertiesPluginDescriptorFinder implements PluginDescriptorFinder
     protected void validatePluginDescriptor(PluginDescriptor pluginDescriptor) throws PluginException {
         if (StringUtils.isEmpty(pluginDescriptor.getPluginId())) {
             throw new PluginException("plugin.id cannot be empty");
-
         }
         if (StringUtils.isEmpty(pluginDescriptor.getPluginClass())) {
             throw new PluginException("plugin.class cannot be empty");
         }
+        if (pluginDescriptor.getVersion() == null) {
+            throw new PluginException("plugin.version cannot be empty");
+        }
     }
 
 }