I was seeing Warning: Invalid argument supplied for foreach() in element_children() being thrown as a result of _webform_encrypt_decrypt_nested_values() calling itself recursively with $component = NULL.
This was happening with a multi-page form containing fieldsets. When the fieldset is on a non-current page, _webform_client_form_add_component() still processes it provided that it has children (see the end of that function).
When the children also turn out to not be part of the current page (no surprise there), what we're left with is a component for the fieldset with the value NULL, so _webform_encrypt_decrypt_nested_values() picks that up and tries to process it, calling element_children() and generating the error.
This feels like a webform bug, but we can easily protect against it here.
(Cross-referencing with #2065649: NULL parent components on multi-page forms → )
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Given the assertion in #2 (also closing related webform issue #2065649: NULL parent components on multi-page forms → ), plus the fact that the function being patched here no longer exists in current versions of the webform_encrypt, this issue can be closed.