responses: fix EvaluateResponse serialization

dap/src/responses.rs

@@ -70,10 +70,11 @@ pub struct EvaluateResponse {
   /// The type of the evaluate result.
   /// This attribute should only be returned by a debug adapter if the
   /// corresponding capability `supportsVariableType` is true.
-  #[serde(rename = "type")]
+  #[serde(rename = "type", skip_serializing_if = "Option::is_none")]
   pub type_field: Option<String>,
   /// Properties of an evaluate result that can be used to determine how to
   /// render the result in the UI.
+  #[serde(skip_serializing_if = "Option::is_none")]
   pub presentation_hint: Option<VariablePresentationHint>,
   /// If `variablesReference` is > 0, the evaluate result is structured and its
   /// children can be retrieved by passing `variablesReference` to the
@@ -84,17 +85,20 @@ pub struct EvaluateResponse {
   /// The client can use this information to present the variables in a paged
   /// UI and fetch them in chunks.
   /// The value should be less than or equal to 2147483647 (2^31-1).
+  #[serde(skip_serializing_if = "Option::is_none")]
   pub named_variables: Option<i64>,
   /// The i64 of indexed child variables.
   /// The client can use this information to present the variables in a paged
   /// UI and fetch them in chunks.
   /// The value should be less than or equal to 2147483647 (2^31-1).
+  #[serde(skip_serializing_if = "Option::is_none")]
   pub indexed_variables: Option<i64>,
   /// A memory reference to a location appropriate for this result.
   /// For pointer type eval results, this is generally a reference to the
   /// memory address contained in the pointer.
   /// This attribute should be returned by a debug adapter if corresponding
   /// capability `supportsMemoryReferences` is true.
+  #[serde(skip_serializing_if = "Option::is_none")]
   pub memory_reference: Option<String>,
 }