Update wireEmpty() function so that it also returns false when giving a NullPage or NullField object. Add WireNull interface for future Null objects.

wire/core/Functions.php

@@ -1087,6 +1087,7 @@ function wireCount($value) {
  * 
  * - It returns true for Countable objects that have 0 items. 
  * - It considers whitespace-only strings to be empty.
+ * - It considers WireNull objects (like NullPage or any others) to be empty (3.0.149+).
  * - You cannot pass it an undefined variable without triggering a PHP warning. 
  * 
  * ~~~~~
@@ -1117,6 +1118,7 @@ function wireEmpty($value) {
 	if(empty($value)) return true;
 	if(is_object($value)) {
 		if($value instanceof \Countable && !count($value)) return true;
+		if($value instanceof WireNull) return true; // 3.0.149+
 	} else if(is_string($value)) {
 		if(!strlen(trim($value))) return true;
 	}

wire/core/Interfaces.php

@@ -327,6 +327,12 @@ interface WirePageEditor {
 	public function getPage(); 	
 }
 
+/**
+ * Interface shared by all ProcessWire Null objects
+ *
+ */
+interface WireNull { }
+
 /**
  * Interface that indicates the object supports its items being paginated
  * 

wire/core/NullField.php

@@ -10,7 +10,7 @@
  *
  */
 
-class NullField extends Field {
+class NullField extends Field implements WireNull {
 	public function get($key) {
 		if($key == 'id') return 0;
 		if($key == 'name') return '';

wire/core/NullPage.php

@@ -32,7 +32,7 @@
  *
  */
 
-class NullPage extends Page {
+class NullPage extends Page implements WireNull {
 	/**
 	 * #pw-internal
 	 *