Delete keys with value nothing in addenv.

NEWS.md

@@ -69,6 +69,7 @@ New library features
 * `@testset foo()` can now be used to create a test set from a given function. The name of the test set
   is the name of the called function. The called function can contain `@test` and other `@testset`
   definitions, including to other function calls, while recording all intermediate test results. ([#42518])
+* Keys with value `nothing` are now removed from the environment in `addenv` ([#43271]).
 
 Standard library changes
 ------------------------

base/cmd.jl

@@ -256,6 +256,7 @@ setenv(cmd::Cmd; dir="") = Cmd(cmd; dir=dir)
 Merge new environment mappings into the given [`Cmd`](@ref) object, returning a new `Cmd` object.
 Duplicate keys are replaced.  If `command` does not contain any environment values set already,
 it inherits the current environment at time of `addenv()` call if `inherit` is `true`.
+Keys with value `nothing` are deleted from the env.
 
 See also [`Cmd`](@ref), [`setenv`](@ref), [`ENV`](@ref).
 
@@ -274,7 +275,11 @@ function addenv(cmd::Cmd, env::Dict; inherit::Bool = true)
         end
     end
     for (k, v) in env
-        new_env[string(k)::String] = string(v)::String
+        if v === nothing
+            delete!(new_env, string(k)::String)
+        else
+            new_env[string(k)::String] = string(v)::String
+        end
     end
     return setenv(cmd, new_env)
 end

test/spawn.jl

@@ -817,6 +817,10 @@ end
         cmd2 = addenv(cmd, "FOO" => "foo2", "BAR" => "bar"; inherit=true)
         @test strip(String(read(cmd2))) == "foo2 bar"
     end
+    # Keys with value === nothing are deleted
+    cmd = Cmd(`$shcmd -c "echo \$FOO \$BAR"`, env=Dict("FOO" => "foo", "BAR" => "bar"))
+    cmd2 = addenv(cmd, "FOO" => nothing)
+    @test strip(String(read(cmd2))) == "bar"
 end