Here is my prepare SELECT statement:
----
[Prepared Select Statement] SELECT ('EmailAddress=' + CAST(EmailAddress AS VARCHAR)) as a1 from StoreShop.Trainers WHERE EmailAddress=?+'@'+?
----
with:
Parameter values: ${ID},${EMAIL-GROUP}
Parameter types: VARCHAR,VARCHAR

Here is a bulk of data and how JDBC sample is responding for them:

1) {"",""}(two empty strings - not null)
AR: the sample is failing: Response message: java.sql.SQLException: number of arguments (0) and number of types (2) are not equal
ER: Response data: {"a1"} - data are not found but "a1" is a column name - not java-exception error;

2) {"aaa6",""} - the second parameter is empty string
AR: the sample is failing: Response message: java.sql.SQLException: number of arguments (1) and number of types (2) are not equal
ER:  Response data: {"a1"} - data are not found but "a1" is a column name - not java-exception error;

3) {"","bluerealm.com"} - the first parameter is empty string
AR: Response data: {"a1"} as expected - data not found but "a1" in a column name;

So, JDBC sample is working inconsistency in three similar cases.

My expectation is that in the cases #1&#2 test-results are same as in the #3.