question: public void add ( String fieldName , String value ) { if ( fieldName == null ) throw new IllegalArgumentException ( "fieldname == null" ) ; if ( value == null ) throw new IllegalArgumentException ( "value == null" ) ; if ( fieldName . length ( ) == 0 || fieldName . indexOf ( '\0' ) != - 1 || value . indexOf ( '\0' ) != - 1 ) { throw new IllegalArgumentException ( "Unexpected header: " + fieldName + ": " + value ) ; } addLenient ( fieldName , value ) ; }
target:  Add a field with the specified value. 