Question: dsolve problem when dealing with a simple system of differential equations for plot?

r := 1;
c := 1;
G := 1;
M := 1;
theta := 90;

ex1 := {
Diff(f1(t), t$2)
+ 2*(-G*M/(r*(-r*c^2+2*G*M)))*Diff(f(t), t1)*Diff(f2(t), t) = 0,

Diff(f2(t), t$2)
+ (-(-r*c^2+2*G*M)*G*M/(r^3*c^4))*Diff(f1(t), t)^2
+ (G*M/(r*(-r*c^2+2*G*M)))*Diff(f2(t), t$2)
+ ((-r*c^2+2*G*M)/c^2)*Diff(f3(t), t$2)
+ ((-r*c^2+2*G*M)*sin(theta)^2/c^2)*Diff(f4(t), t)^2 = 0,

Diff(f3(t), t$2)
+ (-sin(theta)*cos(theta))*Diff(f4(t), t)^2 = 0,

Diff(f3(t), t$2)
+ 2*(1/r)*Diff(f2(t), t)*Diff(f4(t), t)
+ 2*(cos(theta)/sin(theta))*Diff(f3(t), t)*Diff(f4(t), t) = 0

};

dsol := dsolve(ex1, {f1(t),f2(t),f3(t),f4(t)});

ic := {f1(0)=0, f2(0)=0, f3(0)=0, f4(0)=0, D(f1)(0)=0, D(f2)(0)=0, D(f3)(0)=0, D(f4)(0)=0};
dsol := dsolve({ex1, ic}, numeric);

> dsol := dsolve({ex1, ic}, numeric);
Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations

dsol := dsolve(ex1 union ic, numeric);

Warning, The use of global variables in numerical ODE problems is deprecated, and will be removed in a future release. Use the 'parameters' argument instead (see ?dsolve,numeric,parameters)
Warning, variable f(t) is present in the input system, but not in the reduced system. It will not be present in the solution.
proc(x_rkf45_dae)  ...  end;


with(plots):
odeplot(dsol, [t, f(t)], 0..100);