Could not initialize class org.codehaus.groovy.reflection.ReflectionCache unity code example

Example: java.lang.NoClassDefFoundError: Could not initialize class org.codehaus.groovy.vmplugin.v7.Java7

It's probably because you use Gradle as the build system and JDK14
and the Gradle version is old. Reference:

https://github.com/gradle/gradle/issues/10248

If you use Gradle Wrapper then refer to
$PROJECT_ROOT/gradle/wrapper/gradle-wrapper.properties.
Property distributionUrl should be: 

distributionUrl=https\://services.gradle.org/distributions/gradle-6.3-bin.zip

If it's an older version then change it, run ./gradlew clean build 
and try again.