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We present the results of a study of the vortex lattice of the nickel chalcogenide superconductor TlNi2Se2, using small angle neutron scattering. This is a heavy-fermion superconductor with the same crystal symmetry as the iron-arsenides. Previous work points to it being a two-gap superconductor, with an unknown pairing mechanism. No structural transitions in the vortex lattice are seen in the phase diagram, and only small variations in the anisotropy. Modeling of the form factor and penetration depth indicates that this material is an unconventional superconductor, with nodes in the gap structure. arXiv:1808.03207v1 [cond-mat.supr-con]