"Cannot read property 'xxx' of null"

I've got a document fragment with children that开发者_如何学运维 I want to loop over (when possible). This is causing an error "Cannot read property 'xxx' of null".

How do I test if this will be the case?

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You may want to do the following:

if ((documentFragment !== null) && documentFragment.hasOwnProperty('xxx')) {
    // handle property xxx of documentFragment as required
}