WindowsStorage: getGermline returns NULL if the window doesn't exist

algo/core/windows.cpp

@@ -23,7 +23,10 @@ string WindowsStorage::getLabel(junction window) {
 }
 
 Germline *WindowsStorage::getGermline(junction window) {
-  return germline_by_window[window];   
+  map<junction, Germline *>::iterator result = germline_by_window.find(window);
+  if (result == germline_by_window.end())
+    return NULL;
+  return result->second;
 }
 
 JsonList WindowsStorage::statusToJson(junction window) {

algo/core/windows.h

@@ -39,6 +39,10 @@ class WindowsStorage {
    */
   WindowsStorage(map<string, string> &labels);
 
+  /**
+   * @return a pointer to the germline of the window
+   *         or NULL if the window doesn't exist.
+   */
   Germline *getGermline(junction window);
   
   JsonList statusToJson(junction window);