question: default Configuration withSystemProperties ( Function < String , String > propertyNameConverter ) { Properties props = asProperties ( ) ; Properties systemProperties = System . getProperties ( ) ; for ( String key : systemProperties . stringPropertyNames ( ) ) { String propName = propertyNameConverter . apply ( key ) ; if ( propName != null && propName . length ( ) > 0 ) { String value = systemProperties . getProperty ( key ) ; props . setProperty ( propName , value ) ; } } return from ( props ) ; }
target:  Return a copy of this configuration except where acceptable system properties are used to overwrite properties copied from this configuration. Each of the system properties is examined and passed to the supplied function; if the result of the function is a non-null string, then a property with that string as the name and the system property value are added to the returned configuration.