NiFi Attribute toNumber failing validation

[#1]

I used the update attribute to create an attribute called compressvalue and set it to 2. Then I used this attribute in the posthttp processor Attribute Compression Level and used my attribute $(compressvalue:toNumber()). The processor fails to validate complaining my attribute is not an integer. any ideas?

[#2 · Accepted solution]

The Compression Level property doesn't look like it supports expression language. The docs should say which properties do.