canignore.hh: use default member initializer and defaulted con- and destructor

dune/solvers/common/canignore.hh

@@ -18,9 +18,7 @@ public:
     /**
      * \brief Default constructor
      */
-    CanIgnore()
-        : ignoreNodes_(nullptr)
-    {}
+    CanIgnore() = default;
 
     /**
      * \brief Constructor from bit vector
@@ -36,8 +34,7 @@ public:
      *
      * Does NOT delete the bitfield!
      */
-    ~CanIgnore()
-    {}
+    ~CanIgnore() = default;
 
     /**
      * \brief Set bit vector
@@ -68,7 +65,7 @@ public:
     /**
      * \brief A flag for each degree of freedom stating whether the dof should be ignored by the solver
      */
-    const BitVectorType* ignoreNodes_;
+    const BitVectorType* ignoreNodes_ = nullptr;
 
 };