NullPointerException in Ed25519FieldElement.invert

[mckpm]

We occasionally see this crash in the field (haven't managed to reproduce):

#0. Crashed: main
       at net.i2p.crypto.eddsa.spec.EdDSANamedCurveTable.getByName(EdDSANamedCurveTable.java:67)
       at org.stellar.sdk.KeyPair.(KeyPair.java:29)
       at org.stellar.sdk.KeyPair.fromAccountId(KeyPair.java:104)
[...]

Fatal Exception: java.lang.ExceptionInInitializerError
       at net.i2p.crypto.eddsa.spec.EdDSANamedCurveTable.getByName(EdDSANamedCurveTable.java:67)
       at org.stellar.sdk.KeyPair.(KeyPair.java:29)
       at org.stellar.sdk.KeyPair.fromAccountId(KeyPair.java:104)
[...]

Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'b.a.a.a.a.e b.a.a.a.a.e.g()' on a null object reference
       at net.i2p.crypto.eddsa.math.ed25519.Ed25519FieldElement.invert(Ed25519FieldElement.java:811)
       at net.i2p.crypto.eddsa.math.GroupElement.precompute(GroupElement.java:472)
       at net.i2p.crypto.eddsa.math.Curve.createPoint(Curve.java:78)
       at net.i2p.crypto.eddsa.spec.EdDSANamedCurveTable.(EdDSANamedCurveTable.java:43)
       at net.i2p.crypto.eddsa.spec.EdDSANamedCurveTable.getByName(EdDSANamedCurveTable.java:67)
       at org.stellar.sdk.KeyPair.(KeyPair.java:29)
       at org.stellar.sdk.KeyPair.fromAccountId(KeyPair.java:104)
[...]

[str4d]

invert() is being called here:

https://github.com/str4d/ed25519-java/blob/581c6a969a54180632d6991ef7a5a0b7a3e95524/src/net/i2p/crypto/eddsa/math/GroupElement.java#L467-L472

At the crash point, invert() is doing this:

https://github.com/str4d/ed25519-java/blob/581c6a969a54180632d6991ef7a5a0b7a3e95524/src/net/i2p/crypto/eddsa/math/ed25519/Ed25519FieldElement.java#L806-L812

So my initial guess would be that t2.square() returns null at some point either before or during that loop, and the subsequent iteration then has t2 set to null, causing the NPE. However, Ed25519FieldElement.square() never returns null (it does deterministic maths and then calls a constructor, which can never return null but does potentially throw an IAE). So... I'm going to leave this open until someone else can reproduce this.