Index: wp-includes/class-wp-network.php
===================================================================
--- wp-includes/class-wp-network.php	(revision 40723)
+++ wp-includes/class-wp-network.php	(working copy)
@@ -162,7 +162,7 @@
 				return (int) $this->blog_id;
 		}
 
-		return null;
+		return isset( $this->$key ) ? $this->$key : null;
 	}
 
 	/**
@@ -184,7 +184,7 @@
 				return true;
 		}
 
-		return false;
+		return isset( $this->$key );
 	}
 
 	/**
Index: wp-includes/class-wp-site.php
===================================================================
--- wp-includes/class-wp-site.php	(revision 40723)
+++ wp-includes/class-wp-site.php	(working copy)
@@ -251,7 +251,7 @@
 				}
 		}
 
-		return null;
+		return isset( $this->$key ) ? $this->$key : null;
 	}
 
 	/**
@@ -290,7 +290,7 @@
 				}
 		}
 
-		return false;
+		return isset( $this->$key );
 	}
 
 	/**