Create polynomial of order 0 with Taylor1([Type], 0) (#402)

* Fix bug for `Taylor1(T, 0)` (with test)

* Bump patch version

Author: lbenet

Project.toml

@@ -1,6 +1,6 @@
 name = "TaylorSeries"
 uuid = "6aa5eb33-94cf-58f4-a9d0-e4b2c4fc25ea"
-version = "0.21.2"
+version = "0.21.3"
 repo = "https://github.com/JuliaDiff/TaylorSeries.jl.git"
 
 [deps]

src/constructors.jl

@@ -83,12 +83,14 @@ julia> Taylor1(Rational{Int}, 4)
 ```
 """
 function Taylor1(::Type{T}, order::Int) where {T<:Number}
+    order == 0 && return Taylor1{T}(FixedSizeVectorDefault{T}([zero(T)]))
     coeffs = FixedSizeVectorDefault{T}(undef, order+1)
     coeffs .= zero(T)
     coeffs[2] = one(T)
     return Taylor1{T}(coeffs)
 end
 function Taylor1(order::Int)
+    order == 0 && return Taylor1{Float64}(FixedSizeVectorDefault{Float64}([0.0]))
     coeffs = FixedSizeVectorDefault{Float64}(undef, order+1)
     coeffs .= 0.0
     coeffs[2] = 1.0

test/onevariable.jl

@@ -105,6 +105,8 @@ Base.iszero(::SymbNumber) = false
     @test y.coeffs[1:2:9] == rv[1:5]
     @test_throws AssertionError y[0:2:3] = rv
 
+    @test Taylor1(0) == Taylor1(0.0, 0)
+    @test Taylor1(Rational{Int}, 0) == Taylor1(0//1, 0)
     @test Taylor1([0,1,0,0]) == Taylor1(3)
     @test getcoeff(Taylor1(Complex{Float64},3),1) == complex(1.0,0.0)
     @test Taylor1(Complex{Float64},3)[1] == complex(1.0,0.0)