Failing dictionary keys as variables

Stack trace

ERROR: key not found: "x"
 in getindex at dict.jl:615
 in getindex at no file
 in include at /Applications/Julia-0.3.0.app/Contents/Resources/julia/lib/julia/sys.dylib
 in include_from_node1 at loading.jl:128
 in process_options at /Applications/Julia-0.3.0.app/Contents/Resources/julia/lib/julia/sys.dylib
 in _start at /Applications/Julia-0.3.0.app/Contents/Resources/julia/lib/julia/sys.dylib (repeats 2 times)
while loading /path/to/file/test.jl, in expression starting on line 239

test.jl

using JuMP

m = Model()
vars = Dict()
# Adding below still does not work
# vars["x"] = 0
# vars["y"] = 0

@defVar(m, 0 <= vars["x"] <= 2)
@defVar(m, 0 <= vars["y"] <= 30)

@setObjective(m, Max, 5* vars["x"] + 3*vars["y"])
@addConstraint(m, 1*vars["x"]+ 5*vars["y"] <= 3.0)

print(m)

status = solve(m)

println("Objective value: ", getObjectiveValue(m))
println("x = ", getValue(vars["x"]))
println("y = ", getValue(vars["y"])