Thymeleaf no longer processes results of standard Java stream methods

[d4span]

After a recent upgrade of Spring Boot and Thymeleaf to version 3.1.1 and 3.1.2, respectively, we are suddenly experiencing exceptions of the following type in several Thymeleaf templates that worked fine before the upgrade:

org.springframework.expression.EvaluationException: Accessing member 'isEmpty' is forbidden for type 'class java.util.ImmutableCollections$ListN' in Thymeleaf expressions. 
Blocked classes are: [...]. Allowed classes are: [...].

The collection causing this issue results from a standard Java Streams .toList() method invocation.

Is there a way to configure the list of allowed classes to avoid these issues with results of core library methods?

[jmiguelsamper]

Hi @d4span ,

Could you check that your templates contain invocations of "isEmpty()" instead of just "isEmpty" (without parenthesis).

I came with the same error this morning and the cause was the missing parenthesis.