Get 35mmfocallength Metadata

I tried to get the Metadata for 35mm equivalent focal length in a script I provided here: Image info data in Viewer.
The line
var foc = item.metadata.image_text.focallength;
is working fine whereas the line
var foc = item.metadata.image_text.35mmfocallength;
doesn't work but always throws an error. Is this a bug or am I doing something wrong?