How to increment address of the register in the Ruby language?

I am trying to increment the address of the register by using the increment operator in Ruby.But it is throwing error like 'can't convert fixnum into the string'.Can i use the increment operator to increment the address of the register.

Error: test_write_memory_value(TestRemoteSalad): TypeError: can't convert Fixnum into String D:/Vidyanath/sc_165/fruit-salad/src/targets/RemoteSalad.rb:1649:in +' D:/Vidyanath/sc_165/fruit-salad/src/targets/RemoteSalad.rb:1649:inblock in write_memory_value' D:/Vidyanath/sc_165/fruit-salad/src/targets/RemoteSalad.rb:1647:in each' D:/Vidyanath/sc_165/fruit-salad/src/targets/RemoteSalad.rb:1647:inwrite_memory_value' test/test_remote_salad.rb:150:in `test_write_memory_value'

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