code: def all_agents(stmts):
      
      agents = []
      for stmt in stmts:
          for agent in stmt.agent_list():
              # Agents don't always have a TEXT db_refs entry (for instance
              # in the case of Statements from databases) so we check for this.
              if agent is not None and agent.db_refs.get('TEXT') is not None:
                  agents.append(agent)
      return agents
docs: Return a list of all of the agents from a list of statements.
  
      Only agents that are not None and have a TEXT entry are returned.
  
      Parameters
      ----------
      stmts : list of :py:class:`indra.statements.Statement`
  
      Returns
      -------
      agents : list of :py:class:`indra.statements.Agent`
          List of agents that appear in the input list of indra statements.