Unrelated problem in physics.units

[1e9abhi1e10]

from sympy.physics.units import convert_to
from sympy.physics.units.systems.cgs import cgs_gauss
from sympy.physics.units.definitions.unit_definitions import  coulomb,  erg, volt, joule, meter, newton, statvolt
from sympy.physics.units.definitions.unit_definitions import statcoulomb as esu

print(convert_to(volt, joule/coulomb)) 
# it gives joule/coulomb

print(convert_to(volt/meter, newton/coulomb)) 
# it gives newton/coulomb

print(convert_to(statvolt, erg/esu)) 
# but it gives statvolt

[shishir-11]

def _get_conversion_matrix_for_expr(expr, target_units, unit_system):
    from sympy.matrices.dense import Matrix

    dimension_system = unit_system.get_dimension_system()

    expr_dim = Dimension(unit_system.get_dimensional_expr(expr))
    dim_dependencies = dimension_system.get_dimensional_dependencies(expr_dim, mark_dimensionless=True)
    target_dims = [Dimension(unit_system.get_dimensional_expr(x)) for x in target_units]
    canon_dim_units = [i for x in target_dims for i in dimension_system.get_dimensional_dependencies(x, mark_dimensionless=True)]
    canon_expr_units = set(dim_dependencies)

    if not canon_expr_units.issubset(set(canon_dim_units)):
        return None

    seen = set()
    canon_dim_units = [i for i in canon_dim_units if not (i in seen or seen.add(i))]

    camat = Matrix([[dimension_system.get_dimensional_dependencies(i, mark_dimensionless=True).get(j, 0) for i in target_dims] for j in canon_dim_units])
    exprmat = Matrix([dim_dependencies.get(k, 0) for k in canon_dim_units])

    try:
        res_exponents = camat.solve(exprmat)
    except NonInvertibleMatrixError:
        return None

    return res_exponents

if not canon_expr_units.issubset(set(canon_dim_units)):
return None

The problem occurs here . Why are we doing this ?
Removing this keeps rest of the results same but gives

>>> print(convert_to(statvolt, erg/esu))
1