Only specify error handler if one exists

Summary: Broke open source and some other tests because the error handler is defined in Buck2 repo, so not all toolchains would have an error handler defined. Will look at making error handler be able to take in a `None` but doing this for now to unbreak tests.

Reviewed By: christolliday

Differential Revision: D71658974

fbshipit-source-id: f29f17b883241a51c09cd89baaf0294683dea998

Author: Will-MingLun-Li

prelude/python/make_py_package.bzl

@@ -374,6 +374,11 @@ def _make_py_package_impl(
         # Inplace par should be built locally to avoid materialization cost
         prefer_local = (standalone and package_python_locally(ctx, python_toolchain)) or not standalone
 
+        # only specify error_handler if one exists
+        error_handler_args = {}
+        if python_toolchain.python_error_handler:
+            error_handler_args["error_handler"] = python_toolchain.python_error_handler
+
         cmd = cmd_args(
             make_py_package_cmd if make_py_package_cmd != None else python_toolchain.make_py_package_standalone,
         )
@@ -389,7 +394,7 @@ def _make_py_package_impl(
             category = "par",
             identifier = identifier_prefix.format(output_suffix),
             allow_cache_upload = allow_cache_upload,
-            error_handler = python_toolchain.python_error_handler,
+            **error_handler_args
         )
 
     else:

prelude/python/source_db.bzl

@@ -48,8 +48,13 @@ def create_dbg_source_db(
         args = dependencies,
     ))
 
+    # only specify error_handler if one exists
+    error_handler_args = {}
+    if python_toolchain.python_error_handler:
+        error_handler_args["error_handler"] = python_toolchain.python_error_handler
+
     artifacts.append(dep_manifests.project_as_args("source_artifacts"))
-    ctx.actions.run(cmd, category = "py_dbg_source_db", error_handler = python_toolchain.python_error_handler)
+    ctx.actions.run(cmd, category = "py_dbg_source_db", **error_handler_args)
 
     return DefaultInfo(default_output = output, other_outputs = artifacts)