Merge pull request #1424 from LukasKorba/1420-Synchronizer-proposeShi…

…elding-crashes-when-there-are-insufficient-funds-to-shield

[#1420] Synchronizer.proposeShielding crashes when there are insuffic…

CHANGELOG.md

@@ -6,6 +6,9 @@ and this library adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+## Fixed
+- The backend method proposeShielding checks the pointer for a null value before attempting to construct the Data with it. Without this check, proposeShielding would crash when there were either zero funds to shield or when the amount was less than the threshold defined by the client.
+
 # 2.1.5 - 2024-04-18
 
 ## Changed

Sources/ZcashLightClientKit/Rust/ZcashRustBackend.swift

@@ -752,11 +752,15 @@ struct ZcashRustBackend: ZcashRustBackendWelding {
         )
 
         guard let proposal else {
-            throw ZcashError.rustShieldFunds(lastErrorMessage(fallback: "`proposeShielding` failed with unknown error"))
+            throw ZcashError.rustShieldFunds(lastErrorMessage(fallback: "Failed with nil proposal."))
         }
 
         defer { zcashlc_free_boxed_slice(proposal) }
-
+
+        guard proposal.pointee.ptr != nil else {
+            throw ZcashError.rustShieldFunds(lastErrorMessage(fallback: "Failed with nil pointer."))
+        }
+
         return try FfiProposal(contiguousBytes: Data(
             bytes: proposal.pointee.ptr,
             count: Int(proposal.pointee.len)