Add an example snippet query

ql/examples/snippets/emptythen.ql

@@ -0,0 +1,18 @@
+/**
+ * @name If statements with empty then branch
+ * @description Finds 'if' statements where the 'then' branch is
+ *              an empty block statement
+ * @id ruby/examples/emptythen
+ * @tags if
+ *       then
+ *       empty
+ *       conditional
+ *       branch
+ *       statement
+ */
+
+import ruby
+
+from IfExpr i
+where not exists(i.getThen().getAChild())
+select i