fixes

openmdao/core/explicitcomponent.py

@@ -68,7 +68,7 @@ def _configure(self):
         """
         new_jacvec_prod = getattr(self, 'compute_jacvec_product', None)
 
-        if self.matrix_free is _UNDEFINED:
+        if self.matrix_free == _UNDEFINED:
             self.matrix_free = overrides_method('compute_jacvec_product', self, ExplicitComponent)
 
         if self.matrix_free:

openmdao/core/implicitcomponent.py

@@ -76,7 +76,7 @@ def _configure(self):
         if self._has_solve_nl is _UNDEFINED:
             self._has_solve_nl = overrides_method('solve_nonlinear', self, ImplicitComponent)
 
-        if self.matrix_free is _UNDEFINED:
+        if self.matrix_free == _UNDEFINED:
             self.matrix_free = overrides_method('apply_linear', self, ImplicitComponent)
 
         if self.matrix_free:

openmdao/solvers/solver.py

@@ -217,8 +217,12 @@ def msginfo(self):
         str
             Info to prepend to messages.
         """
+        # Default initialization
         if self._system is None:
             return type(self).__name__
+        # Following Dead Weakref
+        elif self._system() is None:
+            return type(self).__name__
         return f"{type(self).__name__} in {self._system().msginfo}"
 
     def _inf_nan_failure(self):
@@ -307,8 +311,13 @@ def _setup_solvers(self, system, depth):
         depth : int
             depth of the current system (already incremented).
         """
+        # Default initialization
         if self._system is None:
             self._system = weakref.ref(system)
+        # Following Dead Weakref
+        elif self._system() is None:
+            self._system = weakref.ref(system)
+        # Assignment Mismatch
         elif self._system != weakref.ref(system):
             raise RuntimeError(f"{type(self).__name__} has already been assigned to "
                                f"{self._system().msginfo} and cannot also be assigned to "