Added 'strict' parameter for template retrieval

LLama/Exceptions/RuntimeError.cs

@@ -77,6 +77,21 @@ public MissingTemplateException(string message)
     } 
 }
 
+/// <summary>
+/// `llama_decode` return a non-zero status code
+/// </summary>
+public class TemplateNotFoundException
+    : RuntimeError
+{
+    /// <inheritdoc />
+    public TemplateNotFoundException(string name)
+        : base($"llama_model_chat_template failed: Tried to retrieve template '{name}' but it couldn't be found.\n" +
+                                            $"This might mean that the model was exported incorrectly, or that this is a base model that contains no templates.\n" +
+                                            $"This exception can be disabled by passing 'strict=false' as a parameter when retrieving the template.")
+    {
+    } 
+}
+
 /// <summary>
 /// `llama_get_logits_ith` returned null, indicating that the index was invalid
 /// </summary>

LLama/LLamaTemplate.cs

@@ -105,19 +105,21 @@ public bool AddAssistant
     /// <summary>
     /// Construct a new template, using the default model template
     /// </summary>
-    /// <param name="model"></param>
-    /// <param name="name"></param>
-    public LLamaTemplate(SafeLlamaModelHandle model, string? name = null)
-        : this(model.GetTemplate(name))
+    /// <param name="model">The native handle of the loaded model.</param>
+    /// <param name="name">The name of the template, in case there are many or differently named. Set to 'null' for the default behaviour of finding an appropriate match.</param>
+    /// <param name="strict">Setting this to true will cause the call to throw if no valid templates are found.</param>
+    public LLamaTemplate(SafeLlamaModelHandle model, string? name = null, bool strict = true)
+        : this(model.GetTemplate(name, strict))
     {
     }
 
     /// <summary>
     /// Construct a new template, using the default model template
     /// </summary>
-    /// <param name="weights"></param>
-    public LLamaTemplate(LLamaWeights weights)
-        : this(weights.NativeHandle)
+    /// <param name="weights">The handle of the loaded model's weights.</param>
+    /// <param name="strict">Setting this to true will cause the call to throw if no valid templates are found.</param>
+    public LLamaTemplate(LLamaWeights weights, bool strict = true)
+        : this(weights.NativeHandle, strict: strict)
     {
     }
 

LLama/Native/SafeLlamaModelHandle.cs

@@ -603,15 +603,22 @@ internal IReadOnlyDictionary<string, string> ReadMetadata()
         /// Get the default chat template. Returns nullptr if not available
         /// If name is NULL, returns the default chat template
         /// </summary>
-        /// <param name="name"></param>
+        /// <param name="name">The name of the template, in case there are many or differently named. Set to 'null' for the default behaviour of finding an appropriate match.</param>
+        /// <param name="strict">Setting this to true will cause the call to throw if no valid templates are found.</param>
         /// <returns></returns>
-        public string? GetTemplate(string? name = null)
+        public string? GetTemplate(string? name = null, bool strict = true)
         {
             unsafe
             {
                 var bytesPtr = llama_model_chat_template(this, name);
                 if (bytesPtr == null)
-                    return null;
+                {
+                    if (strict)
+                        throw new TemplateNotFoundException(name ?? "default template");
+                    else
+                        return null;
+
+                }
 
                 // Find null terminator
                 var spanBytes = new Span<byte>(bytesPtr, int.MaxValue);