GROOVY-6887: AutoClone issue with CompileStatic
GROOVY-6887: AutoClone issue with CompileStatic (additional tests plus tidy doco)
GROOVY-6889: clean up generated code when using @AutoExternalize with @CompileStatic
doco tweaks and tidy up for GROOVY-6889 and GROOVY-6887
GROOVY-6893: clean up generated code when using @EqualsAndHashCode with @CompileStatic
GROOVY-6894: clean up generated code when using @TupleConstructor with @CompileStatic
GROOVY-6895: Add null check to avoid errors to be swallowed