Fix: Empty CLI string defaults no longer override env/API config

[dc-larsen]

Summary

• Fixes a bug where CLI argument defaults (empty strings) were incorrectly overwriting values loaded from environment variables and the Socket Basics API dashboard config
• Changes the condition from if arg_value is not None to if arg_value for non-bool types

Problem

When CLI arguments with empty string defaults (like --dockerfiles) are not explicitly provided by the user, they were overwriting non-empty values from:

1. Environment variables (e.g., INPUT_DOCKERFILES set via GitHub Actions workflow)
2. Socket Basics API config (dashboard settings)

This caused Dockerfile scanning to fail even when correctly configured in the dashboard with dockerfiles: "Dockerfile", because the CLI default of "" would wipe out that value.

Root Cause

# Before: empty string passes this check
if arg_value is not None:
    config_dict[param_name] = arg_value  # Overwrites with ""

Fix

# After: empty string is falsy, won't override
if arg_value:
    config_dict[param_name] = arg_value

Test plan

• Verified dashboard API returns correct dockerfiles: "Dockerfile" value
• Test Dockerfile scanning with dashboard config only (no workflow input)
• Test Dockerfile scanning with explicit workflow input
• Test that explicit CLI args still override when provided