Guard Conditions are not recognized

[polarene]

Describe the bug

A block of code having a when() with guard conditions is incorrectly reported as an error.

Example code:

when (val node = path.node) {
    // Handle property declarations (val/const val)
    is PropertyDeclaration if node.initializerExpression != null -> addIfValid(node.initializerExpression!!)
    // ...
}

the relevant part of error log:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':diktatCheck'.
> 124:44 Expecting '->'

Notice the reported text position is at the first character of if.

Expected behavior

Code passes checks

Observed behavior

• Code fails the check
• The message reports an error but no specific rule is violated
• The Diktat reports are empty

Steps to Reproduce

1. Write a block of code using when with guards
2. run gradle diktatCheck

Environment information

• diktat version: 2.0.0
• build tool (maven/gradle): gradle
• how is diktat run (CLI, plugin, etc.): plugin
• kotlin version: 2.2.21
• operating system: MacOS 26.2