fix: should keep mappings field (#102)

Author: JSerFeng

src/source.rs

@@ -337,8 +337,7 @@ struct RawSourceMap {
   pub sources_content: Option<Vec<Option<Cow<'static, str>>>>,
   #[serde(skip_serializing_if = "Option::is_none")]
   pub names: Option<Vec<Option<Cow<'static, str>>>>,
-  #[serde(skip_serializing_if = "Option::is_none")]
-  pub mappings: Option<String>,
+  pub mappings: String,
 }
 
 impl RawSourceMap {
@@ -424,7 +423,7 @@ impl TryFrom<RawSourceMap> for SourceMap {
       .collect();
     Ok(Self {
       file: raw.file,
-      mappings: raw.mappings.unwrap_or_default(),
+      mappings: raw.mappings,
       sources,
       sources_content,
       names,
@@ -462,7 +461,7 @@ impl From<SourceMap> for RawSourceMap {
           .map(|s| (!s.is_empty()).then_some(s))
           .collect(),
       ),
-      mappings: (!map.mappings.is_empty()).then_some(map.mappings),
+      mappings: map.mappings,
     }
   }
 }