NiFi: expression to test if attribute exists

Question

I need to optionally use an attribute if it exists, in an expression. I know I can use ifelse to determine this, however the attribute name is printed as a literal if it doesn't exist.

What is the correct expression to test for this?

${MyOptionalAttribute:notnull():ifElse(MyOptionalAttribute,'my default value')}

Answer 1

Use a UpdateAttribute processor:

• MyOptionalAttribute (dynamic property): ${MyOptionalAttribute:notNull():ifElse(${MyOptionalAttribute}, "default value")}