v2.12.1

Fixed

• Fixed bug where properties on OpenXmlCompositeElement instances could not be set to null to remove element (#850)
• Fixed OpenXmlElement.RawOuterXml to properly set null values without throwing (#818)
• Allow rewriting of all malformed URIs regardless of target value (#835)

Thanks to the following for their contributions for this release:

@akindle
@aidilumarov