Improve docstring

python/core/auto_generated/qgsmaplayer.sip.in

@@ -1490,7 +1490,10 @@ Sets the coordinate transform context to ``transformContext``
 
     QgsProject *project() const;
 %Docstring
-Returns the parent project if available.
+Returns the parent project if this map layer is added to a project.
+Otherwise returns ``None``
+
+.. versionadded:: 3.18
 %End
 
   signals:

src/core/qgsmaplayer.h

@@ -1336,7 +1336,10 @@ class CORE_EXPORT QgsMapLayer : public QObject
 #endif
 
     /**
-     * Returns the parent project if available.
+     * Returns the parent project if this map layer is added to a project.
+     * Otherwise returns NULLPTR
+     *
+     * \since QGIS 3.18
      */
     QgsProject *project() const;