AK: StringBuilder with 0 initial capacity shouldn't build null String

With 0 initial capacity, we don't allocate an underlying ByteBuffer
for the StringBuilder, which would then lead to a null String() being
returned from to_string().

This patch makes sure we always build a valid String.

1 files changed, 9 insertions, 0 deletions

diff --git a/AK/Tests/TestString.cpp b/AK/Tests/TestString.cpp
index bd9a8fbc73..5576bcec90 100644
--- a/AK/Tests/TestString.cpp
+++ b/AK/Tests/TestString.cpp
@@ -199,4 +199,13 @@ TEST_CASE(split)
     EXPECT_EQ(parts[2].characters()[3], '\0');
 }
 
+TEST_CASE(builder_zero_initial_capacity)
+{
+   StringBuilder builder(0);
+   builder.append("");
+   auto built = builder.build();
+   EXPECT_EQ(built.is_null(), false);
+   EXPECT_EQ(built.length(), 0u);
+}
+
 TEST_MAIN(String)