Fiw role serialization, Ollama 2.5 + does not accept anymore in upper…

… case.

model-providers/ollama/runtime/src/main/java/io/quarkiverse/langchain4j/ollama/Role.java

@@ -1,10 +1,13 @@
 package io.quarkiverse.langchain4j.ollama;
 
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 
 import io.quarkiverse.langchain4j.ollama.runtime.jackson.RoleDeserializer;
+import io.quarkiverse.langchain4j.ollama.runtime.jackson.RoleSerializer;
 
 @JsonDeserialize(using = RoleDeserializer.class)
+@JsonSerialize(using = RoleSerializer.class)
 public enum Role {
 
     SYSTEM,

model-providers/ollama/runtime/src/main/java/io/quarkiverse/langchain4j/ollama/runtime/jackson/RoleSerializer.java

@@ -0,0 +1,21 @@
+package io.quarkiverse.langchain4j.ollama.runtime.jackson;
+
+import java.io.IOException;
+import java.util.Locale;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+import io.quarkiverse.langchain4j.ollama.Role;
+
+public class RoleSerializer extends StdSerializer<Role> {
+    public RoleSerializer() {
+        super(Role.class);
+    }
+
+    @Override
+    public void serialize(Role role, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
+        jsonGenerator.writeString(role.toString().toLowerCase(Locale.ROOT));
+    }
+}