Add existing() method that allows for making sure that a configurable actually...

Add existing() method that allows for making sure that a configurable actually exists when executing a method on it.
Usage:
try {
  ->existing()->action();
} catch(FeedsNotExistingException ) {}

Fix notices from setConfig() by making sure that all default values are present.

includes/FeedsConfigurable.inc

@@ -6,6 +6,12 @@
  * FeedsConfigurable and helper functions.
  */
 
+/**
+ * Used when an object does not exist in the DB or code but should.
+ */
+class FeedsNotExistingException extends Exception {
+}
+
 /**
  * A configurable class.
  */
@@ -68,6 +74,17 @@ abstract class FeedsConfigurable {
     $this->disabled = FALSE;
   }
 
+  /**
+   * Determine whether this object is persistent. I. e. it is defined either
+   * in code or in the database.
+   */
+  public function existing() {
+    if ($this->export_type == FEEDS_EXPORT_NONE) {
+      throw new FeedsNotExistingException(t('Object is not persistent.'));
+    }
+    return $this;
+  }
+
   /**
    * Save a configuration. Concrete extending classes must implement a save
    * operation.
@@ -85,12 +102,13 @@ abstract class FeedsConfigurable {
    * Set configuration.
    *
    * @param $config
-   *   Array containing configuration information. Will be filtered by the keys
-   *   returned by configDefaults().
+   *   Array containing configuration information. Config array will be filtered
+   *   by the keys returned by configDefaults() and populated with default
+   *   values that are not included in $config.
    */
   public function setConfig($config) {
-    $default_keys = $this->configDefaults();
-    $this->config = array_intersect_key($config, $default_keys);
+    $defaults = $this->configDefaults();
+    $this->config = array_intersect_key($config, $defaults) + $defaults;
   }
 
   /**