Applied hicpp-use-equals-default clang-tidy fixes

src/common/model/diagram_element.cc

@@ -26,7 +26,7 @@ namespace clanguml::common::model {
 
 std::atomic_uint64_t diagram_element::m_nextId = 1;
 
-diagram_element::diagram_element() { }
+diagram_element::diagram_element() = default;
 
 diagram_element::id_t diagram_element::id() const { return id_; }
 

src/common/types.h

@@ -31,7 +31,7 @@ template <typename T> class optional_ref {
 public:
     using optional_type = T;
 
-    optional_ref() { }
+    optional_ref() = default;
 
     optional_ref(T *value) { value_ = value; }
 

src/sequence_diagram/visitor/call_expression_context.cc

@@ -20,7 +20,7 @@
 
 namespace clanguml::sequence_diagram::visitor {
 
-call_expression_context::call_expression_context() { }
+call_expression_context::call_expression_context() = default;
 
 void call_expression_context::reset()
 {