Fix: Ensure non-nullable Map for FunctionCallPart.args

Resolves a compilation type mismatch: "inferred type is ...HashMap<String, String?>? but Map<String, String?> was expected".
This indicated that the SDK's `FunctionCallPart` constructor expects a non-nullable `Map<String, String?>` for its `args` parameter.

The `PartDto.toSdk()` mapper for `FunctionCallPartDto` has been updated. If the DTO's `args` field is `null`, an empty `Map<String, String?>` is now passed to the `FunctionCallPart` constructor. Otherwise, the DTO's `args` map is converted to a non-nullable `Map<String, String?>`.

This ensures the SDK constructor always receives a non-null Map instance, satisfying the type requirement and fixing the build failure.

Author: google-labs-jules[bot]

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/dtos/PhotoReasoningMappers.kt

@@ -56,13 +56,16 @@ fun PartDto.toSdk(): Part { // No context needed here as path is absolute
         }
         is BlobPartDto -> BlobPart(mimeType = this.mimeType, blob = this.data)
         is FunctionCallPartDto -> {
-            val sdkArgs: HashMap<String, String?>? = this.args?.let { dtoArgs ->
-                // Explicitly create a HashMap.
-                val newMap = hashMapOf<String, String?>()
-                dtoArgs.entries.forEach { entry ->
+            val sdkArgs: Map<String, String?> = if (this.args == null) {
+                emptyMap<String, String?>() // Provide an empty map if DTO.args is null
+            } else {
+                // If DTO.args is not null, create a new map from it.
+                // Values in this.args can be null, matching Map<String, String?>.
+                val newMap = mutableMapOf<String, String?>()
+                this.args.entries.forEach { entry ->
                     newMap[entry.key] = entry.value
                 }
-                newMap
+                newMap.toMap() // Return immutable, non-null map
             }
             FunctionCallPart(name = this.name, args = sdkArgs)
         }