Exception in custom XML loader for RimWorld.BackstoryTrait. Node is:
<li><defName>RE_BioticRecoveryOffset</defName><degree>1</degree><chance>100</chance></li>

Exception is:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: value
at System.Number.ParseSingle (System.String value, System.Globalization.NumberStyles options, System.Globalization.NumberFormatInfo numfmt) [0x00003] in <eae584ce26bc40229c1b1aa476bfa589>:0
at System.Single.Parse (System.String s, System.Globalization.NumberStyles style, System.Globalization.NumberFormatInfo info) [0x00000] in <eae584ce26bc40229c1b1aa476bfa589>:0
at System.Single.Parse (System.String s, System.IFormatProvider provider) [0x0000c] in <eae584ce26bc40229c1b1aa476bfa589>:0
at Verse.ParseHelper.ParseIntPermissive (System.String str) [0x0001a] in <97fedf20253b44c1a698b8198f811fe9>:0
at Verse.ParseHelper.FromString[T] (System.String str) [0x00009] in <97fedf20253b44c1a698b8198f811fe9>:0
at RimWorld.BackstoryTrait.LoadDataFromXmlCustom (System.Xml.XmlNode xmlRoot) [0x00028] in <97fedf20253b44c1a698b8198f811fe9>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke(System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00032] in <eae584ce26bc40229c1b1aa476bfa589>:0
--- End of inner exception stack trace ---
at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00048] in <eae584ce26bc40229c1b1aa476bfa589>:0
at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <eae584ce26bc40229c1b1aa476bfa589>:0
at Verse.DirectXmlToObject.ObjectFromXml[T] (System.Xml.XmlNode xmlRoot, System.Boolean doPostLoad) [0x00088] in <97fedf20253b44c1a698b8198f811fe9>:0
UnityEngine.StackTraceUtility:ExtractStackTrace ()
(wrapper dynamic-method) Verse.Log:Verse.Log.Error_Patch1 (string)
Verse.DirectXmlToObject:ObjectFromXml<RimWorld.BackstoryTrait> (System.Xml.XmlNode,bool)
Verse.DirectXmlToObject:ListFromXml<RimWorld.BackstoryTrait> (System.Xml.XmlNode)
Verse.DirectXmlToObject:ListFromXmlReflection<RimWorld.BackstoryTrait> (System.Xml.XmlNode)
Verse.DirectXmlToObject:ObjectFromXml<System.Collections.Generic.List`1<RimWorld.BackstoryTrait>> (System.Xml.XmlNode,bool)
Verse.DirectXmlToObject:ObjectFromXmlReflection<System.Collections.Generic.List`1<RimWorld.BackstoryTrait>> (System.Xml.XmlNode,bool)
Verse.DirectXmlToObject:ObjectFromXml<AlienRace.AlienBackstoryDef> (System.Xml.XmlNode,bool)
Verse.DirectXmlToObject:ObjectFromXmlReflection<AlienRace.AlienBackstoryDef> (System.Xml.XmlNode,bool)
Verse.DirectXmlLoader:DefFromNode (System.Xml.XmlNode,Verse.LoadableXmlAsset)
Verse.LoadedModManager:ParseAndProcessXML (System.Xml.XmlDocument,System.Collections.Generic.Dictionary`2<System.Xml.XmlNode, Verse.LoadableXmlAsset>)
Verse.LoadedModManager:LoadAllActiveMods ()
Verse.PlayDataLoader:DoPlayLoad ()
Verse.PlayDataLoader:LoadAllPlayData (bool)
Verse.Root/<>c:<Start>b__6_1 ()
Verse.LongEventHandler:RunEventFromAnotherThread (System.Action)
Verse.LongEventHandler/<>c:<UpdateCurrentAsynchronousEvent>b__27_0 ()
System.Threading.ThreadHelper:ThreadStart_Context (object)
System.Threading.ExecutionContext:RunInternal (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool)
System.Threading.ExecutionContext:Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool)
System.Threading.ExecutionContext:Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object)
System.Threading.ThreadHelper:ThreadStart ()