Fix: omit --setting-sources flag when setting_sources is empty or unset

[qing-ant]

Summary

When setting_sources was not provided (None) or was an empty list, the SDK always passed --setting-sources "" to the CLI. The empty string argument causes the CLI argument parser to consume the next flag (e.g. --permission-mode) as the --setting-sources value, producing:

Error processing --setting-sources: Invalid setting source: --permission-mode.
Valid options are: user, project, local

This blocked all default SDK usage without an explicit setting_sources workaround.

Fix

Only add --setting-sources when setting_sources is a non-empty list, matching the pattern used by other array-typed flags (allowed_tools, disallowed_tools, betas).

Before:

sources_value = (
    ",".join(self._options.setting_sources)
    if self._options.setting_sources is not None
    else ""
)
cmd.extend(["--setting-sources", sources_value])  # always emitted

After:

if self._options.setting_sources:
    cmd.extend(["--setting-sources", ",".join(self._options.setting_sources)])

Testing

• Added 3 unit tests verifying the fix:
  • test_build_command_setting_sources_omitted_when_not_provided — no setting_sources → no --setting-sources flag
  • test_build_command_setting_sources_omitted_when_empty — empty [] → no --setting-sources flag
  • test_build_command_setting_sources_included_when_provided — ["user", "project"] → --setting-sources user,project
• All 427 existing tests pass
• Lint clean

Fixes anthropics/claude-agent-sdk-typescript#252