If an entity doesn't have an @prerequisite, it can result in exceptions being thrown.  Also, persistent_maps appears to be order-dependent.

Take host-collections, for example:

===
hammer> import host-collection --csv-file /tmp/exports/system-groups.csv
[ERROR 2014-06-27 18:00:25 Exception] Error: undefined method `keys' for #<Array:0x7f33528536a8>
Error: undefined method `keys' for #<Array:0x7f33528536a8>
[ERROR 2014-06-27 18:00:25 Exception] 

NoMethodError (undefined method `keys' for #<Array:0x7f33528536a8>):
    /root/github/hammer-cli-import/lib/hammer_cli_import/persistentmap.rb:147:in `prune_persistent_maps'
    /root/github/hammer-cli-import/lib/hammer_cli_import/persistentmap.rb:146:in `each'
    /root/github/hammer-cli-import/lib/hammer_cli_import/persistentmap.rb:146:in `prune_persistent_maps'
    /root/github/hammer-cli-import/lib/hammer_cli_import/base.rb:412:in `execute'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:67:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/lib/hammer_cli/./apipie/../abstract.rb:22:in `run'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/subcommand/execution.rb:11:in `execute'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:67:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/lib/hammer_cli/./apipie/../abstract.rb:22:in `run'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/subcommand/execution.rb:11:in `execute'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:67:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/lib/hammer_cli/./apipie/../abstract.rb:22:in `run'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:125:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/lib/hammer_cli/shell.rb:104:in `execute'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:67:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/lib/hammer_cli/./apipie/../abstract.rb:22:in `run'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/subcommand/execution.rb:11:in `execute'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:67:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/lib/hammer_cli/./apipie/../abstract.rb:22:in `run'
    /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:125:in `run'
    /usr/lib/ruby/gems/1.8/gems/hammer_cli-0.1.1/bin/hammer:100
    /usr/bin/hammer:19:in `load'
    /usr/bin/hammer:19
===

Expected behavior:

===
hammer> import host-collection --csv-file /tmp/exports/system-groups.csv
Host_collection [19->243] already imported.
Host_collection [20->244] already imported.
Host_collection [33->245] already imported.
Host_collection [34->246] already imported.
Host_collection [35->247] already imported.
hammer> 
===

2c855c30fbcc26f31925f8afc374a3b3151e0778

Since this issue was entered in Red Hat Bugzilla, the release flag has been
set to ? to ensure that it is properly evaluated for this release.

# hammer import host-collection --csv-file /tmp/exports/system-groups.csv 
[Foreman] username: admin
[Foreman] password for admin: 
Summary
  Created 242 host_collections.
# hammer import host-collection --csv-file /tmp/exports/system-groups.csv 
[Foreman] username: admin
[Foreman] password for admin: 
Summary
  No action taken.

DEVELPER VERIFIED with rubygem-hammer_cli_import-0.10.4-1.1.el6sat.noarch

This was delivered with Satellite 6.0 which was released on 10 September 2014.