Question:How can I fix "Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations" in Maple?

Question:How can I fix "Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations" in Maple?

Maple 2018

>restart;
> ODEtools[declare]((S, L, B)(t), prime = t);
ODEtools[declare](S(t), L(t), B(t), prime = t)
> DE1 := diff(S(t), t) = -L*S*beta-`&mu;S`+mu;
d
DE1 := --- S(t) = -L S beta - &mu;S + mu
dt
> DE2 := diff(L(t), t) = L*S*beta-(gamma+mu)*S;
d
DE2 := --- L(t) = beta S L - (gamma + mu) S
dt
> DE3 := diff(B(t), t) = L*gamma-gamma*mu;
d
DE3 := --- B(t) = L gamma - gamma mu
dt
> init_conds := S(0) >= 0, L(0) >= 0, B(0) >= 0;
init_conds := 0 <= S(0), 0 <= L(0), 0 <= B(0)
> sys := {init_conds, diff(B(t), t) = L*gamma-gamma*mu, diff(L(t), t) = L*S*beta-(gamma+mu)*S, diff(S(t), t) = -L*S*beta-`&mu;S`+mu};

> sol := dsolve(sys, numeric, parameters = [mu, beta, gamma, S(t), L(t), B(t)], method = rkf45);

Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations

> sol(parameters = [mu = .234, beta = 2.345, gamma = 5.678, S(t) = 6.678, L(t) = 6.789, B(t) = 7.123]);
sol(parameters = [mu = 0.234, beta = 2.345, gamma = 5.678, S(t) = 6.678, L(t) = 6.789, B(t) = 7.123])

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