What does the “{ }” displayed in the output mean?

When I solved the simultaneous equations, the result was derived as "{ }". The input is as follows.

    s /. Out[112]     θ /. Out[113]      {(-((36*a*θ)/(-36 + 9*b^2 + 2*θ^2)^2) + (18*a*     b*θ)/(-36 + 9*b^2 + 2*θ^2)^2 + (2*     a*(-2 + b)*θ)/(-72 + 18*b^2 + 4*θ^2) -      (4*a*(-2 + b)*θ)/(36*(-4 + b^2) +      8*θ^2) - (18*(-2 + b)*θ*     Subscript[c, f])/(-36 + 9*b^2 +      2*θ^2)^2 - (2*(-2 + b)*θ*     Subscript[c, f])/(-72 + 18*b^2 + 4*θ^2) +      (4*θ*((-2 + b)*Subscript[c, f] -       2*Subscript[c, h]))/(36*(-4 + b^2) +      8*θ^2) + (36*θ*     Subscript[c, h])/(-36 + 9*b^2 + 2*θ^2)^2 +      (4*θ*Subscript[c, h])/(-72 + 18*b^2 +      4*θ^2))/((18*θ^2)/(-36 + 9*b^2 +      2*θ^2)^2 - (18*(-2 + b)*(2 + b))/(-72 + 18*b^2 +      4*θ^2) +      (18*(-2 + b)*(2 + b))/(36*(-4 + b^2) + 8*θ^2))}      Out[115]      Rs = Out[114]     Rθ = Out[115]      {(-((36*a*θ)/(-36 + 9*b^2 + 2*θ^2)^2) + (18*a*     b*θ)/(-36 + 9*b^2 + 2*θ^2)^2 + (2*     a*(-2 + b)*θ)/(-72 + 18*b^2 + 4*θ^2) -      (4*a*(-2 + b)*θ)/(36*(-4 + b^2) +     8*θ^2) - (18*(-2 + b)*θ*    Subscript[c, f])/(-36 + 9*b^2 +      2*θ^2)^2 - (2*(-2 + b)*θ*    Subscript[c, f])/(-72 + 18*b^2 + 4*θ^2) +      (4*θ*((-2 + b)*Subscript[c, f] -       2*Subscript[c, h]))/(36*(-4 + b^2) +     8*θ^2) + (36*θ*    Subscript[c, h])/(-36 + 9*b^2 + 2*θ^2)^2 +      (4*θ*Subscript[c, h])/(-72 + 18*b^2 +     4*θ^2))/((18*θ^2)/(-36 + 9*b^2 +      2*θ^2)^2 - (18*(-2 + b)*(2 + b))/(-72 + 18*b^2 +     4*θ^2) +      (18*(-2 + b)*(2 + b))/(36*(-4 + b^2) + 8*θ^2))}     Out[117]     Solve[{s - Rs == 0, θ - Rθ == 0}, {s, θ}]     {} 

If a symbol such as "{ }" appears in the output, what does this mean? When the equation is wrong or the calculation is wrong, does a symbol like "{ }" appear in the output?