only set attributes that are set in the import
only set attributes that are set in the import

this fixes an issue when importing pages that don’t have a is_hidden
field. In that case the is_hidden attribute was set to nil, which isn’t
valid. If the attribute is just skipped, then the default value for the 
attribute is used.
concord-consortium/lara,concord-consortium/lara,concord-consortium/lara,concord-consortium/lara,concord-consortium/lara