Description
When there is no region server available to move regions to, we would see:
Valid region move targets:
TypeError: can't convert nil into String
__for__ at /usr/lib/hbase/bin/region_mover.rb:336
call at org/jruby/RubyProc.java:270
call at org/jruby/RubyProc.java:220
each at file:/usr/lib/hbase/lib/jruby-complete-1.6.5.jar!/builtin/java/java.util.rb:7
unloadRegions at /usr/lib/hbase/bin/region_mover.rb:333
(root) at /usr/lib/hbase/bin/region_mover.rb:471
Better error message / exit code should be provided.