fix: handle null argument in GORM domain class constructor (Groovy 4 regression)

[davydotcom]

Problem

Calling new DomainClass(null) on a GORM domain class throws:

groovy.lang.GroovyRuntimeException: Could not find matching constructor for: DomainClass(null)

This is a regression from Grails 6 / Groovy 3, where new DomainClass(null) was treated equivalently to new DomainClass().

Root Cause

In Groovy 3, the runtime resolved new SomeClass(null) by matching it to the implicit map-based constructor that Groovy provides for POGOs. When null was passed, the runtime simply created the object via the no-arg constructor without setting any properties.

Groovy 4 changed how constructor resolution works at runtime. The implicit map constructor is no longer matched when null is passed as the argument, causing the GroovyRuntimeException.

This is a common pattern in Grails applications — for example, when a variable that may be null is passed to a domain constructor:

def props = maybeGetProperties() // could return null
def obj = new MyDomain(props)    // fails in Grails 7 / Groovy 4

Fix

The GormEntityTransformation (the @Entity AST transform) now injects an explicit Map constructor into every GORM entity class. The constructor:

• Accepts a Map parameter, allowing null to match at runtime
• If the map is not null, sets properties via InvokerHelper.setProperties(this, args) — the same mechanism Groovy uses internally for map constructors
• If null, does nothing (equivalent to the no-arg constructor)
• Also ensures a no-arg constructor is preserved, since adding any explicit constructor prevents Groovy from auto-generating the default one

The constructor is injected early in the transformation (before trait composition), so trait \$init\$ methods are properly wired into it by the Groovy trait composer.

Tests

Added NullConstructorArgSpec in grails-data-hibernate5/core with three tests:

1. No-arg constructor works (baseline)
2. Null constructor argument works the same as no-arg
3. Domain created with null constructor argument can be saved

All 598 existing hibernate5 core tests continue to pass with 0 failures.

Co-Authored-By: Oz oz-agent@warp.dev

[jdaugherty]

Closing this, i think teh core issue was the rest transforms weren't included in your project.