Don't set blanks

builder_core.go

@@ -118,7 +118,8 @@ func (rb *Builder) Param(key string, values ...string) *Builder {
 }
 
 // ParamOptional sets a query parameter on a Builder's URL
-// only if it is not set by some other call to Param or ParamOptional.
+// only if it is not set by some other call to Param or ParamOptional
+// and one of the values is a non-blank string.
 func (rb *Builder) ParamOptional(key string, values ...string) *Builder {
 	rb.ub.ParamOptional(key, values...)
 	return rb
@@ -131,7 +132,8 @@ func (rb *Builder) Header(key string, values ...string) *Builder {
 }
 
 // HeaderOptional sets a header on a request
-// only if it has not already been set by another call to Header or HeaderOptional.
+// only if it has not already been set by another call to Header or HeaderOptional
+// and one of the values is a non-blank string.
 func (rb *Builder) HeaderOptional(key string, values ...string) *Builder {
 	rb.rb.HeaderOptional(key, values...)
 	return rb

core_req.go

@@ -89,7 +89,9 @@ func (rb *requestBuilder) Request(ctx context.Context, u *url.URL) (req *http.Re
 		}
 	}
 	for _, kv := range rb.headers {
-		if kv.optional && req.Header.Get(kv.key) == "" {
+		if kv.optional &&
+			req.Header.Get(kv.key) == "" &&
+			minitrue.Or(kv.values...) != "" {
 			req.Header[http.CanonicalHeaderKey(kv.key)] = kv.values
 		}
 	}

core_url.go

@@ -78,7 +78,9 @@ func (ub *urlBuilder) URL() (u *url.URL, err error) {
 			}
 		}
 		for _, kv := range ub.params {
-			if kv.optional && q.Get(kv.key) == "" {
+			if kv.optional &&
+				q.Get(kv.key) == "" &&
+				minitrue.Or(kv.values...) != "" {
 				q[kv.key] = kv.values
 			}
 		}