Extension for line level freight term

Summary:
we have requirement to get the first shippable line 'Freight Term' and derive the shipping method based on that freight term. we are trying use extension to get this done. However, We are not able to retrieve FreightTerms Name from the lines.getAttribute("FreightTerms") in Sales order extension

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Code Snippet (add any code snippets that support your topic, if applicable):

import oracle.apps.scm.doo.common.extensions.ValidationException;
import oracle.apps.scm.doo.common.extensions.Message;
def lines = header.getAttribute("Lines");
while (lines.hasNext())