Improve documentation for get_animation()

doc/classes/AnimationPlayer.xml

@@ -67,7 +67,7 @@
 			<return type="Animation" />
 			<argument index="0" name="name" type="String" />
 			<description>
-				Returns the [Animation] with key [code]name[/code] or [code]null[/code] if not found.
+				Returns the [Animation] with the key [code]name[/code]. If the animation does not exist, [code]null[/code] is returned and an error is logged.
 			</description>
 		</method>
 		<method name="get_animation_list" qualifiers="const">

scene/animation/animation_player.cpp

@@ -1052,13 +1052,15 @@ void AnimationPlayer::rename_animation(const StringName &p_name, const StringNam
 bool AnimationPlayer::has_animation(const StringName &p_name) const {
 	return animation_set.has(p_name);
 }
+
 Ref<Animation> AnimationPlayer::get_animation(const StringName &p_name) const {
-	ERR_FAIL_COND_V(!animation_set.has(p_name), Ref<Animation>());
+	ERR_FAIL_COND_V_MSG(!animation_set.has(p_name), Ref<Animation>(), vformat("Animation not found: \"%s\".", p_name));
 
 	const AnimationData &data = animation_set[p_name];
 
 	return data.animation;
 }
+
 void AnimationPlayer::get_animation_list(List<StringName> *p_animations) const {
 	List<String> anims;