String getCountry() {
      return "";
    }
the graph looks like the following.
number in parentheses () indicates number of stream partitions.
number in parentheses in quotes ("") indicates expected partition count.
number in square brackets [] indicates operator ID.

input3 (32) -> filter [7] -> partitionBy [8] ("64") -> map [10] -> join [14] -> sendTo(output2) [15] (16)
                                                                  |
             input2 (16) -> partitionBy [3] ("64") -> filter [5] -| -> sink [13]
                                                                  |
                                        input1 (64) -> map [1] -> join [11] -> sendTo(output1) [12] (8)
samza-core/src/test/java/org/apache/samza/execution/TestJobGraphJsonGenerator.java