Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self,
                   'credential_type') and self.credential_type is not None:
            _dict['credential_type'] = self.credential_type
        if hasattr(self, 'client_id') and self.client_id is not None:
            _dict['client_id'] = self.client_id
        if hasattr(self, 'enterprise_id') and self.enterprise_id is not None:
            _dict['enterprise_id'] = self.enterprise_id
        if hasattr(self, 'url') and self.url is not None:
            _dict['url'] = self.url
        if hasattr(self, 'username') and self.username is not None:
            _dict['username'] = self.username
        if hasattr(self,
                   'organization_url') and self.organization_url is not None:
            _dict['organization_url'] = self.organization_url
        if hasattr(self, 'site_collection_path'
                  ) and self.site_collection_path is not None:
            _dict['site_collection.path'] = self.site_collection_path
        if hasattr(self, 'client_secret') and self.client_secret is not None:
            _dict['client_secret'] = self.client_secret
        if hasattr(self, 'public_key_id') and self.public_key_id is not None:
            _dict['public_key_id'] = self.public_key_id
        if hasattr(self, 'private_key') and self.private_key is not None:
            _dict['private_key'] = self.private_key
        if hasattr(self, 'passphrase') and self.passphrase is not None:
            _dict['passphrase'] = self.passphrase
        if hasattr(self, 'password') and self.password is not None:
            _dict['password'] = self.password
        if hasattr(self, 'gateway_id') and self.gateway_id is not None:
            _dict['gateway_id'] = self.gateway_id
        if hasattr(self, 'source_version') and self.source_version is not None:
            _dict['source_version'] = self.source_version
        if hasattr(
                self,
                'web_application_url') and self.web_application_url is not None:
            _dict['web_application_url'] = self.web_application_url
        if hasattr(self, 'domain') and self.domain is not None:
            _dict['domain'] = self.domain
        if hasattr(self, 'endpoint') and self.endpoint is not None:
            _dict['endpoint'] = self.endpoint
        if hasattr(self, 'access_key_id') and self.access_key_id is not None:
            _dict['access_key_id'] = self.access_key_id
        if hasattr(self,
                   'secret_access_key') and self.secret_access_key is not None:
            _dict['secret_access_key'] = self.secret_access_key
        return _dict