如果为空，如何为参数设置默认值？

如果运行时中未提供参数，我需要将其设置SYSTEM DATE为默认值load_date。我可以通过检查传递的值并根据 NULL 检查相应地分配它来实现这一点。是否有内置功能来实现这一目标？

我什至尝试使用 if_null 步骤，这似乎是一个问题。

这是我在日志中得到的

2017/11/10 14:19:13 - Spoon - Transformation opened.
2017/11/10 14:19:13 - Spoon - Launching transformation [123]...
2017/11/10 14:19:13 - Spoon - Started the transformation execution.
2017/11/10 14:19:13 - 123 - Dispatching started for transformation [123]
2017/11/10 14:19:19 - get_variables.0 - Finished processing (I=0, O=0, R=1, W=1, U=0, E=0)
2017/11/10 14:19:19 - Write to log.0 - 
2017/11/10 14:19:19 - Write to log.0 - ------------> Linenr 1------------------------------
2017/11/10 14:19:19 - Write to log.0 - load_date = null
2017/11/10 14:19:19 - Write to log.0 - 
2017/11/10 14:19:19 - Write to log.0 - ====================
2017/11/10 14:19:19 - get_system_info.0 - Finished processing (I=0, O=0, R=1, W=1, U=0, E=0)
2017/11/10 14:19:19 - if_null.0 - Finished processing (I=0, O=0, R=1, W=1, U=0, E=0)
2017/11/10 14:19:19 - Write to log.0 - Finished processing (I=0, O=0, R=1, W=1, U=0, E=0)
2017/11/10 14:19:22 - Spoon - The transformation has finished!!

这就是我的转变的样子。在图片中嵌入每个步骤的详细信息。