'as boolean' coercion on null/absent property evaluates to null in assertion blocks (Groovy 5)

Describe the bug

In Spock then: or expect: blocks, using the as boolean operator on a null value or missing map entry—even when explicitly parenthesized—fails to coerce the value to false.

In standard Groovy 5, (null as boolean) == false evaluates to true. However, inside a Spock assertion block in spock-2.4-groovy-5.0, the AST rewriter bypasses the boolean coercion step, leaving the expression as null == false and causing the condition to fail.

To Reproduce

Run the following Specification with spock-core:2.4-groovy-5.0 and groovy:5.0.x:

import spock.lang.Specification

class AsBooleanGroovy5BugSpec extends Specification {

    def "as boolean cast should coerce null map entry to false in assertion block"() {
        given:
        def result = [error: true]

        expect:
        (result.success as boolean) == false
    }
}

Expected behavior

(result.success as boolean) should evaluate to false via Groovy Truth coercion, making false == false pass.

Actual behavior

The test fails with a ConditionNotSatisfiedError. Spock evaluates the left operand as null instead of false:

Condition not satisfied:

(result.success as boolean) == false
 |      |                   |
 |      null                false
 [error:true]

``

Java version

• Spock Version: 2.4-groovy-5.0
• Groovy Version: 5.0.x
• JDK Version: 17+

Buildtool version

------------------------------------------------------------
Gradle 9.6.0
------------------------------------------------------------

Build time:    2026-06-18 23:19:03 UTC
Revision:      3f750f03d77e42327c5f9fcb9992110088330a32

Kotlin:        2.3.21
Groovy:        4.0.32
Ant:           Apache Ant(TM) version 1.10.17 compiled on April 6 2026
Launcher JVM:  25.0.4 (BellSoft 25.0.4+9-LTS)
Daemon JVM:    /home/x/.sdkman/candidates/java/25.0.4-librca (no Daemon JVM specified, using current Java home)
OS:            Linux 6.17.0-1032-oem amd64

What operating system are you using

Linux

Dependencies

org.spockframework:spock-core:2.4-groovy-5.0
+--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT
|    \--- org.apache.grails:grails-bom:8.0.0-SNAPSHOT
|         +--- testCompileClasspath (requested org.apache.grails:grails-bom:8.0.0-M5)
|         +--- edu.berkeley.calnet.grails.plugins:registry-settings:3.0.0-SNAPSHOT
|         |    \--- testCompileClasspath
|         +--- edu.berkeley.calnet.grails.plugins:calnet-ui:3.0.0-SNAPSHOT (requested org.apache.grails:grails-bom:8.0.0-M5)
|         |    \--- testCompileClasspath
|         +--- edu.berkeley.calnet.grails.plugins:ucb-spring-security-cas-ldap:5.0.0-SNAPSHOT
|         |    \--- testCompileClasspath
|         +--- edu.berkeley.calnet.grails.plugins:registry-rest-client:3.0.0-SNAPSHOT (requested org.apache.grails:grails-bom:8.0.0-M5)
|         |    \--- testCompileClasspath
|         \--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
+--- org.apache.grails:grails-bom:8.0.0-SNAPSHOT (*)
+--- org.apache.grails:grails-testing-support-views-gson:8.0.0-SNAPSHOT
|    +--- testCompileClasspath (requested org.apache.grails:grails-testing-support-views-gson)
|    \--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
+--- org.apache.grails.testing:grails-test-core:8.0.0-SNAPSHOT
|    +--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
|    \--- org.apache.grails.testing:grails-testing-support-core:8.0.0-SNAPSHOT
|         +--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
|         \--- org.apache.grails:grails-testing-support-web:8.0.0-SNAPSHOT
|              +--- testCompileClasspath (requested org.apache.grails:grails-testing-support-web)
|              \--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
\--- org.spockframework:spock-bom:2.4-groovy-5.0
     +--- org.apache.grails:grails-base-bom:8.0.0-SNAPSHOT (*)
     +--- org.apache.grails:grails-bom:8.0.0-SNAPSHOT (*)
     \--- org.spockframework:spock-core:2.4-groovy-5.0 (*)

org.spockframework:spock-core -> 2.4-groovy-5.0
\--- testCompileClasspath

Additional context

Work-around

Because as boolean is stripped/ignored by the condition rewriter under Groovy 5, use explicit null checking or defaulting instead:

• Elvis Operator: (result.success ?: false) == false
• Map Defaulting: result.get('success', false) == false
• Groovy Truth Assertion: !result.success

Start by running the supplied AsBooleanGroovy5BugSpec reproduction with Spock 2.4-groovy-5.0 and Groovy 5. Trace the assertion-block AST rewriter to determine where the parenthesized as boolean expression is bypassed; done means the reproduction passes and null or absent map values coerce to false.