fix MutableLinkedList when appending empty list - #915

136 docstrings not included in the manual: Base.push! :: Union{Tuple{IntDisjointSet{T}}, Tuple{T}} where T<:Integer Base.push! :: Union{Tuple{T}, Tuple{DisjointSet{T}, T}} where T Base.push! :: Tuple{BinaryHeap, Any} Base.push! :: Union{Tuple{D}, Tuple{K}, Tuple{SortedDict{K, D}, Pair}} where {K, D} Base.push! :: Union{Tuple{D}, Tuple{K}, Tuple{SortedMultiDict{K, D}, Pair}} where {K, D} Base.push! :: Union{Tuple{T}, Tuple{CircularBuffer{T}, Any}} where T Base.push! :: Union{Tuple{K}, Tuple{RBTree{K}, Any}} where K Base.pop! :: Union{Tuple{V}, Tuple{K}, Tuple{RobinDict{K, V}, Any, Any}} where {K, V} Base.pop! :: Tuple{OrderedRobinDict, Any, Any} Base.pop! :: Tuple{BinaryHeap} Base.pop! :: Tuple{BinaryMinMaxHeap} Base.pop! :: Tuple{SwissDict, Any} Base.pop! :: Tuple{CircularBuffer} Base.size :: Tuple{CircularBuffer} DataStructures.counter :: Tuple{Any} DataStructures.dec! :: Union{Tuple{FenwickTree, Integer}, Tuple{FenwickTree, Integer, Any}} DataStructures.dec! :: Tuple{Accumulator, Any, Number} DataStructures.search_node :: Tuple{Any, Any} Base.in :: Union{Tuple{T}, Tuple{K}, Tuple{Any, Base.KeySet{K, T}}} where {K, T<:(DefaultDict{K})} Base.in :: Union{Tuple{T}, Tuple{K}, Tuple{Any, Base.KeySet{K, T}}} where {K, T<:(DefaultOrderedDict{K})} Base.haskey :: Union{Tuple{K}, Tuple{RBTree{K}, K}} where K Base.haskey :: Tuple{SwissDict, Any} Base.haskey :: Tuple{RobinDict, Any} Base.haskey :: Tuple{OrderedRobinDict, Any} Base.isempty :: Tuple{BinaryHeap} Base.isempty :: Tuple{CircularBuffer} DataStructures.prefixsum :: Union{Tuple{T}, Tuple{FenwickTree{T}, Integer}} where T DataStructures.FenwickTree :: Union{Tuple{AbstractVector{U}}, Tuple{U}} where U DataStructures.heappop! :: Union{Tuple{AbstractArray}, Tuple{AbstractArray, Base.Order.Ordering}} DataStructures.RobinDict Base.empty! :: Tuple{CircularBuffer} DataStructures.popmin! :: Tuple{BinaryMinMaxHeap, Integer} DataStructures.popmin! :: Tuple{BinaryMinMaxHeap} Base.length :: Tuple{BinaryHeap} Base.length :: Tuple{CircularBuffer} DataStructures.top_with_handle :: Tuple{MutableBinaryHeap} DataStructures.right_rotate! :: Tuple{RBTree, DataStructures.RBTreeNode} DataStructures.popall! :: Tuple{BinaryMinMaxHeap} DataStructures.FasterForward Base.first :: Tuple{BinaryHeap} Base.first :: Tuple{BinaryMinMaxHeap} Base.first :: Tuple{CircularDeque} Base.first :: Tuple{CircularBuffer} DataStructures.heappush! :: Union{Tuple{AbstractArray, Any}, Tuple{AbstractArray, Any, Base.Order.Ordering}} DataStructures.num_groups :: Tuple{DisjointSet} DataStructures.num_groups :: Tuple{IntDisjointSet} Base.pushfirst! :: Tuple{CircularDeque, Any} Base.pushfirst! :: Tuple{CircularBuffer, Any} DataStructures.isheap :: Union{Tuple{AbstractArray}, Tuple{AbstractArray, Base.Order.Ordering}} DataStructures.Accumulator Base.union! :: Union{Tuple{T}, Tuple{IntDisjointSet{T}, T, T}} where T<:Integer Base.union! :: Union{Tuple{T}, Tuple{DisjointSet{T}, T, T}} where T DataStructures.nextreme :: Union{Tuple{T}, Tuple{Base.Order.Ordering, Int64, AbstractVector{T}}} where T DataStructures.nlargest :: Tuple{Accumulator} DataStructures.nlargest :: Tuple{Int64, AbstractVector} DataStructures.fix_insert! :: Tuple{RBTree, DataStructures.RBTreeNode} DataStructures.DiBitVector DataStructures.DiBitVector :: Tuple{Integer} Base.resize! :: Tuple{CircularBuffer, Integer} DataStructures.DisjointSet DataStructures.reset! :: Union{Tuple{V}, Tuple{Accumulator{<:Any, V}, Any}} where V DataStructures.children_and_grandchildren :: Union{Tuple{T}, Tuple{T, T}} where T<:Integer Base.get :: Union{Tuple{V}, Tuple{K}, Tuple{RobinDict{K, V}, Any, Any}} where {K, V} Base.get :: Union{Tuple{V}, Tuple{K}, Tuple{Union{Function, Type}, RobinDict{K, V}, Any}} where {K, V} Base.get :: Union{Tuple{V}, Tuple{K}, Tuple{OrderedRobinDict{K, V}, Any, Any}} where {K, V} Base.get :: Unio