Trying to run a DC power flow in pandapower

Question

Using this minimal_example the pandapower devs made slightly modified as an example, here is the ac power flow:

import pandapower as pp
import pandas as pd

#create empty net
net = pp.create_empty_network()

#create buses
bus1 = pp.create_bus(net, vn_kv=20., name="Bus 1")
bus2 = pp.create_bus(net, vn_kv=0.4, name="Bus 2")
bus3 = pp.create_bus(net, vn_kv=0.4, name="Bus 3")

#create bus elements
pp.create_ext_grid(net, bus=bus1, vm_pu=1.02, name="Grid Connection")
pp.create_load(net, bus=bus3, p_mw=0.100, q_mvar=0.05, name="Load")

#create branch elements
trafo = pp.create_transformer(net, hv_bus=bus1, lv_bus=bus2, std_type="0.4 MVA 20/0.4 kV", name="Trafo")
line = pp.create_line(net, from_bus=bus2, to_bus=bus3, length_km=0.1, std_type="NAYY 4x50 SE", name="Line")

pp.runpp(net, max_iteration=500)
#pp.rundcpp(net, numba = False)

net.res_line
net.res_trafo
bus_results = pd.merge(net.bus[['name']], net.res_bus, left_index=True, right_index=True)
print(bus_results)

The printed bus results would be this:

    name     vm_pu  va_degree      p_mw    q_mvar
0  Bus 1  1.020000   0.000000 -0.107265 -0.052675
1  Bus 2  1.008843  -0.760126  0.000000  0.000000
2  Bus 3  0.964431   0.115859  0.100000  0.050000

And res_line would be this:

   p_from_mw  q_from_mvar  p_to_mw  q_to_mvar     pl_mw   ql_mvar  i_from_ka  \
0   0.105392     0.050696     -0.1      -0.05  0.005392  0.000696   0.167325   

    i_to_ka      i_ka  vm_from_pu  va_from_degree  vm_to_pu  va_to_degree  \
0  0.167326  0.167326    1.008843       -0.760126  0.964431      0.115859   

   loading_percent  
0       117.835208 

Now if i remove the # from pp.rundcpp and comment pp.runpp, the DC power flow bus results would be:

    name  vm_pu   va_degree  p_mw  q_mvar
0  Bus 1    NaN    0.000000  -0.1     NaN
1  Bus 2    NaN -150.834866   0.0     NaN
2  Bus 3    NaN -151.132088   0.1     NaN

And res_line would be:

   p_from_mw  q_from_mvar  p_to_mw  q_to_mvar  pl_mw  ql_mvar  i_from_ka  \
0        0.1          0.0     -0.1        0.0    0.0      0.0   0.144338   

    i_to_ka      i_ka  vm_from_pu  va_from_degree  vm_to_pu  va_to_degree  \
0  0.144338  0.144338         1.0     -150.834866       1.0   -151.132088   

   loading_percent  
0       101.646174  

I know that in DC power flow the voltage is always 1 V p.u for every bus but it says "nan", is this normal? Also, there's a big difference between the voltage angle in DC and AC simulations (-0.76 in AC and -150 in DC for bus 2).

The line loading is also a bit different