Don't join on empty values.

Co-authored-by: Steve Dower <[email protected]>

Author: xhochy

Tools/jit/_llvm.py

@@ -73,7 +73,7 @@ async def _get_brew_llvm_prefix(llvm_version: str, *, echo: bool = False) -> str
 @_async_cache
 async def _find_tool(tool: str, llvm_version: str, *, echo: bool = False) -> str | None:
     # Explicitly defined LLVM installation location
-    if (llvm_tools_dir := os.getenv("LLVM_TOOLS_INSTALL_DIR")) is not None:
+    if llvm_tools_dir := os.getenv("LLVM_TOOLS_INSTALL_DIR")):
         path = os.path.join(llvm_tools_dir, tool)
         if await _check_tool_version(path, llvm_version, echo=echo):
             return path