Can I query a parameter and then use it in a where clause when the field it compares to is set for Randomized Encryption in a secure enclave?

Question

I have a table where some columns are encrypted using Randomized Encryption. I'm using a secure enclave and can save and query records fine. I am writing a stored procedure that takes a few parameters and gets records matching the values. Here's a simplified, contrived example where the FirstName and LastName fields are encrypted.

CREATE OR ALTER PROC SearchForPerson
  @FirstName NVARCHAR(512),
  @LastName NVARCHAR(512)
AS
BEGIN
  IF @LastName != ''
    -- select * from Person where LastName = @LastName;
  select * from Person where FirstName = @FirstName;
END

Note the select statement that's commented out. This will save the SP with no errors. If I uncomment that statement, I'll get an error (the line numbers are not real; this is just a sample):

Msg 33277, Level 16, State 6, Procedure SearchForPerson, Line 6
Encryption scheme mismatch for columns/variables '@LastName'. The 
encryption scheme for the columns/variables is (encryption_type = 
'PLAINTEXT') and the expression near line '8' expects it to be 
Randomized, , a BIN2 collation for string data types, and an enclave- 
enabled column encryption key, or PLAINTEXT.
Msg 8180, Level 16, State 1, Procedure sp_describe_parameter_encryption, Line 1
Statement(s) could not be prepared.

Is there a way to test for a valid value of the parameter and then also use it to filter the data? Note this is a very contrived example; in reality, the If statement would be a bit more complex.