Control: *global* snippet changed from NULL to \0 to be distinguished from ''

Author: dg

src/Application/UI/Control.php

@@ -107,7 +107,7 @@ public function flashMessage($message, $type = 'info')
 	public function redrawControl($snippet = NULL, $redraw = TRUE)
 	{
 		if ($redraw) {
-			$this->invalidSnippets[$snippet] = TRUE;
+			$this->invalidSnippets[$snippet === NULL ? "\0" : $snippet] = TRUE;
 
 		} elseif ($snippet === NULL) {
 			$this->invalidSnippets = [];
@@ -162,7 +162,7 @@ public function isControlInvalid($snippet = NULL)
 			}
 
 		} else {
-			return isset($this->invalidSnippets[NULL]) || isset($this->invalidSnippets[$snippet]);
+			return isset($this->invalidSnippets["\0"]) || isset($this->invalidSnippets[$snippet]);
 		}
 	}