fix(go): fixed panic when stream value is nil (firebase#4102)

Author: apascal07

go/ai/generate.go

@@ -640,6 +640,10 @@ func GenerateDataStream[Out any](ctx context.Context, r api.Registry, opts ...Ge
 				yield(nil, err)
 				return err
 			}
+			// Skip yielding if there's no parseable output yet (e.g., incomplete JSON during streaming).
+			if base.IsNil(streamValue) {
+				return nil
+			}
 			if !yield(&StreamValue[Out, Out]{Chunk: streamValue}, nil) {
 				return errGenerateStop
 			}

go/ai/prompt.go

@@ -950,6 +950,10 @@ func (dp *DataPrompt[In, Out]) ExecuteStream(ctx context.Context, input In, opts
 				yield(nil, err)
 				return err
 			}
+			// Skip yielding if there's no parseable output yet (e.g., incomplete JSON during streaming).
+			if base.IsNil(streamValue) {
+				return nil
+			}
 			if !yield(&StreamValue[Out, Out]{Chunk: streamValue}, nil) {
 				return errGenerateStop
 			}

go/internal/base/misc.go

@@ -18,6 +18,7 @@ package base
 
 import (
 	"net/url"
+	"reflect"
 )
 
 // An Environment is the execution context in which the program is running.
@@ -38,3 +39,16 @@ func Zero[T any]() T {
 func Clean(id string) string {
 	return url.PathEscape(id)
 }
+
+// IsNil returns true if v is nil or a nil pointer/interface/map/slice/channel/func.
+func IsNil[T any](v T) bool {
+	rv := reflect.ValueOf(v)
+	switch rv.Kind() {
+	case reflect.Invalid:
+		return true
+	case reflect.Ptr, reflect.Interface, reflect.Map, reflect.Slice, reflect.Chan, reflect.Func:
+		return rv.IsNil()
+	default:
+		return false
+	}
+}