Replace String comparisons with "", String() to is_empty()

Also:
- Adds two stress tests to test_string.h
- Changes to .empty() on std::strings

1 files changed, 1 insertions, 1 deletions

diff --git a/scene/animation/animation_tree.cpp b/scene/animation/animation_tree.cpp
index 57c615a6ab..527946b9de 100644
--- a/scene/animation/animation_tree.cpp
+++ b/scene/animation/animation_tree.cpp
@@ -138,7 +138,7 @@ real_t AnimationNode::_pre_process(const StringName &p_base_path, AnimationNode
 void AnimationNode::make_invalid(const String &p_reason) {
 	ERR_FAIL_COND(!state);
 	state->valid = false;
-	if (state->invalid_reasons != String()) {
+	if (!state->invalid_reasons.is_empty()) {
 		state->invalid_reasons += "\n";
 	}
 	state->invalid_reasons += String::utf8("•  ") + p_reason;