Reduce usage of Default::default() to make it easier to refactor.

src/serde/de.rs

@@ -116,7 +116,7 @@ pub fn from_dynamic<'de, T: Deserialize<'de>>(
 
 impl Error for Box<EvalAltResult> {
     fn custom<T: fmt::Display>(err: T) -> Self {
-        LexError::ImproperSymbol(Default::default(), err.to_string())
+        LexError::ImproperSymbol(String::new(), err.to_string())
             .into_err(Position::NONE)
             .into()
     }

src/serde/metadata.rs

@@ -168,7 +168,7 @@ impl From<&crate::module::FuncInfo> for FnMetadata {
                         .to_vec()
                 }
             } else {
-                Default::default()
+                Vec::new()
             },
         }
     }
@@ -198,7 +198,7 @@ impl From<crate::ast::ScriptFnMetadata<'_>> for FnMetadata {
     }
 }
 
-#[derive(Debug, Clone, Default, Serialize)]
+#[derive(Debug, Clone, Serialize)]
 #[serde(rename_all = "camelCase")]
 struct ModuleMetadata {
     #[serde(skip_serializing_if = "BTreeMap::is_empty")]
@@ -210,7 +210,10 @@ struct ModuleMetadata {
 impl ModuleMetadata {
     #[inline(always)]
     pub fn new() -> Self {
-        Default::default()
+        Self {
+            modules: BTreeMap::new(),
+            functions: Vec::new(),
+        }
     }
 }
 
@@ -281,6 +284,6 @@ impl Engine {
     /// 2) Functions in static modules
     /// 3) Functions in global modules (optional)
     pub fn gen_fn_metadata_to_json(&self, include_global: bool) -> serde_json::Result<String> {
-        self.gen_fn_metadata_with_ast_to_json(&Default::default(), include_global)
+        self.gen_fn_metadata_with_ast_to_json(&AST::empty(), include_global)
     }
 }

src/serde/ser.rs

@@ -28,7 +28,7 @@ impl DynamicSerializer {
     #[must_use]
     pub fn new(_value: Dynamic) -> Self {
         Self {
-            _key: Default::default(),
+            _key: Dynamic::UNIT,
             _value,
         }
     }
@@ -83,7 +83,7 @@ impl DynamicSerializer {
 /// # }
 /// ```
 pub fn to_dynamic<T: Serialize>(value: T) -> RhaiResult {
-    let mut s = DynamicSerializer::new(Default::default());
+    let mut s = DynamicSerializer::new(Dynamic::UNIT);
     value.serialize(&mut s)
 }
 
@@ -397,7 +397,7 @@ impl Serializer for &mut DynamicSerializer {
         #[cfg(not(feature = "no_object"))]
         return Ok(StructVariantSerializer {
             variant: _variant,
-            map: Default::default(),
+            map: Map::new(),
         });
         #[cfg(feature = "no_object")]
         return Err(EvalAltResult::ErrorMismatchDataType(