code: PropositionConverter getInstance(Instance proposition)
              throws KnowledgeSourceReadException {
          if (proposition == null) {
              return null;
          } else {
              if (this.converterMap == null) {
                  populateConverterMap();
              }
              Collection<Cls> types = (Collection<Cls>) proposition.getDirectTypes();
              for (Cls cls : types) {
                  PropositionConverter pc = this.converterMap.get(cls);
                  if (pc != null) {
                      return pc;
                  }
              }
              return null;
          }
      }
docs: Gets an appropriate {@link PropositionConverter} for constructing a
  PROTEMPA proposition definition from the given Protege proposition
  instance.
  
  @param proposition a Protege proposition {@link Proposition} instance.
  
  @return an appropriate {@link PropositionConverter} object, or
  <code>null</code> if the given
  <code>proposition</code> is
  <code>null</code>.
  @throws AssertionError if the given
  <code>proposition</code> does not have a type in the Protege
  <code>Proposition</code> class hierarchy.