How to set parameter default value to null in BIP 12c

Summary

How to set parameter default value to null in BIP 12c

Content

Hi

I am using Oracle BI Publisher 12.2.1.2.0  (build:20160906.0632) . I have a parameter named ‘Spec’. Its Data Type is String. I want to set its Default Value to null. When I input null to the Default Value field, the value actually is ‘null’.

Would you please tell how to set the default value to null in BIP 12c?

Thank you very much!