fix: document_symbols throws exception if section name is empty

Author: d-biehl

packages/language_server/src/robotcode/language_server/robotframework/parts/document_symbols.py

@@ -57,7 +57,7 @@ async def visit_Section(self, node: ast.AST) -> None:  # noqa: N802
             return
 
         header = cast(SectionHeader, section.header)
-        if header.name is None:
+        if not header.name:
             return
 
         r = range_from_node(section)