question: public static void writeStringMap ( DataOutput out , @ Nullable Map < String , String > map ) throws IOException { if ( map != null ) { out . writeInt ( map . size ( ) ) ; for ( Map . Entry < String , String > e : map . entrySet ( ) ) { writeUTFStringNullable ( out , e . getKey ( ) ) ; writeUTFStringNullable ( out , e . getValue ( ) ) ; } } else out . writeInt ( - 1 ) ; }
target:  Writes string-to-string map to given data output.