write_yaml don't try to use ParticleType if Particle has no ParticleType
write_yaml don't try to use ParticleType if Particle has no ParticleType

polysimtools/pysimm,plin1112/pysimm,polysimtools/pysimm,mefortunato/pysimm,plin1112/pysimm,mefortunato/pysimm