SPDXTools does not accept exceptions in PackageLicenseInfoFromFiles tag

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exception.tag.txt
When converting an SPDX tag file to rdf using SPDXTools then an error is produced if the PackageLicenseInfoFromFiles tag contains the name of a license exception. The SPDX specification says that this tag captures all the license types, but without the use of expressions. My interpretation of this is that an expression such as GPL-3.0 WITH Classpath-exception-2.0 must be represented by two separate instances of this tag, for example:

PackageLicenseInfoFromFiles: GPL-3.0
PackageLicenseInfoFromFiles: Classpath-exception-2.0

Therefore I think the SPDXTools ought to accept exceptions for this tag.

I have attached this case as an example, which can be run with:

java -jar spdx-tools-2.0.0-jar-with-dependencies.jar TagToRDF exception.tag exception.rdf
The following verifications failed for the SpdxDocument:
Invalid license id 'Classpath-exception-2.0'. Must start with 'LicenseRef-' and made up of the characters from the set 'a'-'z', 'A'-'Z', '0'-'9', '+', '_', '.', and '-'.
Missing required license text for Classpath-exception-2.0

Tag/value file attached.

From Bugzilla Bug 1291

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The SPDX tools currently accept expressions for PackageLicenseInforFromFiles.