Infinite recursion started by Packet.toJSON()

https://github.com/NASA-AMMOS/AIT-Core/blob/196f4c4f175b6caf407ea73776ef9b906b9ea591/ait/core/tlm.py#L444

Here is the beginning of the traceback when Packet.toJSON() is called. It continues forever until the limit for recursion is reached and the process exits. toJSON calls getattr, which tries to evaluate defn.when.eval, which in turn calls getattr through looking for defn.globals, and so getattr continues to be called recursively forever.

Traceback (most recent call last):
  File "size_test.py", line 10, in <module>
    print(packet.toJSON())
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 445, in toJSON
    return { name: getattr(self, name) for name in self._defn.fieldmap }
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 445, in <dictcomp>
    return { name: getattr(self, name) for name in self._defn.fieldmap }
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 351, in __getattr__
    return self._getattr(fieldname)
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 415, in _getattr
    if defn.when is None or defn.when.eval(self):
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 704, in eval
    result  = eval(self._code, packet._defn.globals, context)
  File "<string>", line 1, in <module>
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 487, in __getitem__
    result = self._packet._getattr(name)
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 415, in _getattr
    if defn.when is None or defn.when.eval(self):
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 704, in eval
    result  = eval(self._code, packet._defn.globals, context)
  File "<string>", line 1, in <module>
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 487, in __getitem__
    result = self._packet._getattr(name)
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 415, in _getattr
    if defn.when is None or defn.when.eval(self):
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 704, in eval
    result  = eval(self._code, packet._defn.globals, context)
  File "<string>", line 1, in <module>
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 487, in __getitem__
    result = self._packet._getattr(name)
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 415, in _getattr
    if defn.when is None or defn.when.eval(self):
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 704, in eval
    result  = eval(self._code, packet._defn.globals, context)
  File "<string>", line 1, in <module>
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 487, in __getitem__
    result = self._packet._getattr(name)
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 415, in _getattr
    if defn.when is None or defn.when.eval(self):
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 704, in eval
    result  = eval(self._code, packet._defn.globals, context)
  File "<string>", line 1, in <module>
  File "/Users/awaldron/Projects/ait/ait-core/ait/core/tlm.py", line 487, in __getitem__
    result = self._packet._getattr(name)