Merge pull request #1255 from lamorton/bugfix

Fix for #1253

Author: ChrisRackauckas

src/systems/validation.jl

@@ -42,6 +42,8 @@ get_unit(x::Literal) = screen_unit(getmetadata(x,VariableUnit, unitless))
 get_unit(op::Differential, args) = get_unit(args[1]) / get_unit(op.x)
 get_unit(op::Difference, args) =   get_unit(args[1]) / get_unit(op.t)
 get_unit(op::typeof(getindex),args) = get_unit(args[1])
+get_unit(x::typeof(SciMLBase.NullParameters)) = unitless
+
 function get_unit(op,args) # Fallback
     result = op(1 .* get_unit.(args)...)
     try

test/units.jl

@@ -16,6 +16,7 @@ D = Differential(t)
 @test MT.get_unit(τ) == u"ms"
 @test MT.get_unit(γ) == MT.unitless
 @test MT.get_unit(0.5) == MT.unitless
+@test MT.get_unit(MT.SciMLBase.NullParameters) == MT.unitless
 
 # Prohibited unit types
 @parameters β [unit = u"°"] α [unit = u"°C"] γ [unit = 1u"s"]