Remove definitions of unsafe_get and isnull fallsback

Were added in #287.

README.md

@@ -131,10 +131,6 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * [`normalize`](http://docs.julialang.org/en/latest/stdlib/linalg/?highlight=normalize#Base.normalize) and [`normalize!`](http://docs.julialang.org/en/latest/stdlib/linalg/?highlight=normalize#Base.normalize!), normalizes a vector with respect to the p-norm ([#13681])
 
-* `unsafe_get` returns the `:value` field of a `Nullable` object without any null-check and has a generic fallback for non-`Nullable` argument ([#18484])
-
-* `isnull` has a generic fallback for non-`Nullable` argument
-
 * `transcode` converts between UTF-xx string encodings in Julia 0.5 (as a lightweight
    alternative to the LegacyStrings package) ([#17323])
 
@@ -494,7 +490,6 @@ includes this fix. Find the minimum version from there.
 [#17323]: https://github.com/JuliaLang/julia/issues/17323
 [#17623]: https://github.com/JuliaLang/julia/issues/17623
 [#18082]: https://github.com/JuliaLang/julia/issues/18082
-[#18484]: https://github.com/JuliaLang/julia/issues/18484
 [#18629]: https://github.com/JuliaLang/julia/issues/18629
 [#18727]: https://github.com/JuliaLang/julia/issues/18727
 [#18977]: https://github.com/JuliaLang/julia/issues/18977

src/Compat.jl

@@ -142,14 +142,6 @@ else
     end
 end
 
-# julia#18484
-@static if VERSION < v"0.6.0-dev.848"
-    unsafe_get(x::Nullable) = x.value
-    unsafe_get(x) = x
-    export unsafe_get
-    Base.isnull(x) = false
-end
-
 # julia#18977
 @static if !isdefined(Base, :xor)
     # 0.6

test/runtests.jl

@@ -40,33 +40,6 @@ else
     end
 end
 
-if VERSION < v"0.7.0-DEV.3017"
-    types = [
-        Bool,
-        Float16,
-        Float32,
-        Float64,
-        Int128,
-        Int16,
-        Int32,
-        Int64,
-        Int8,
-        UInt16,
-        UInt32,
-        UInt64,
-        UInt8,
-    ]
-    for T in types
-        # julia#18484, generic isnull, unsafe_get
-        a = one(T)
-        x = Nullable(a, true)
-        @test isequal(unsafe_get(x), a)
-
-        x = Nullable{Array{T}}()
-        @test_throws UndefRefError unsafe_get(x)
-    end
-end
-
 @test xor(1,5) == 4
 @test 1 ⊻ 5 == 4