question: public static < T > String toString ( Collection < T > collection ) { if ( collection == null ) { return "null" ; } if ( collection . isEmpty ( ) ) { return "" ; } StringBuilder buf = new StringBuilder ( ) ; String delimiter = "" ; for ( T t : collection ) { if ( t == null ) { continue ; } buf . append ( delimiter ) ; buf . append ( t ) ; delimiter = ", " ; } return buf . toString ( ) ; }
target:  Returns a list of the elements invoking toString on non-null elements.