When using Navigation SafeArgs 2.4.0-alpha01+ with Kotlin versions before 1.5.0, you get the following:

Unable to find method ''java.lang.String kotlin.text.CharsKt.titlecase(char, java.util.Locale)''
'java.lang.String kotlin.text.CharsKt.titlecase(char, java.util.Locale)'
at

* What went wrong:
Execution failed for task ':app:generateSafeArgsDebug'.
> 'java.lang.String kotlin.text.CharsKt.titlecase(char, java.util.Locale)'

This is because the titleCase API was not added until Kotlin 1.5.0.

In 2.4.0-alpha01+, SafeArgs must be compatible with AGP 4.2.0 and as a result Gradle 6.7.0, which is compatible with Kotlin versions prior to 1.5.0.

We should avoid using titlecase in SafeArgs until we no longer need to support older Kotlin versions. As a workaround, you can update your gradle version to 7.0+.