Check that properties are not set to null (the value null cannot be saved, see crash in forum-11130).

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/branches/3.0@5740 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Core/Project/Src/Services/PropertyService/Properties.cs

@@ -95,6 +95,10 @@ namespace ICSharpCode.Core
 		
 		public void Set<T>(string property, T value)
 		{
+			if (property == null)
+				throw new ArgumentNullException("property");
+			if (value == null)
+				throw new ArgumentNullException("value");
 			T oldValue = default(T);
 			lock (properties) {
 				if (!properties.ContainsKey(property)) {