Add Javadoc

Author: martinbonnin

src/main/java/graphql/execution/ExecutionContext.java

@@ -173,6 +173,11 @@ public ValueUnboxer getValueUnboxer() {
         return valueUnboxer;
     }
 
+    /**
+     * @return true if the current operation should propagate errors in non-null positions
+     * Propagating errors is the default. Error aware clients may opt in returning null in non-null positions
+     * by using the `@errorHandling` directive.
+     */
     @ExperimentalApi
     public boolean propagateErrors() { return propagateErrors; }