CSV, white spaces and data type. Force Float on empty fields

General Usage
16

Just to convert the column to float, this works

julia> isc = CSV.File("isc-gem-cat.csv", header=93, normalizenames=true, limit=5, datarow=125) |> DataFrame
5×31 DataFrame
 Row │ _date                     lat      lon       smajax    sminax    strike   q       depth    unc      q_1     mw       unc_1    q_2     s        ⋯
     │ String                    Float64  Float64   String    String    String   String  Float64  Float64  String  Float64  Float64  String  String   ⋯
─────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1 │  1905-07-23 20:35:04.13    49.35     96.215     17.8      12.8    173.0    C         10.0     25.0   C         6.19     0.67   C       p       ⋯
   2 │  1905-08-04 05:08:57.25    41.743    19.925     10.3       8.9    180.0    C         15.0      7.2   C         6.19     0.2    C       p
   3 │  1905-09-08 01:43:02.41    38.636    15.784                                C         15.0      6.7   C         7.19     0.2    B       p
   4 │  1905-09-14 19:41:40.64    50.462  -179.492     41.2      26.3    110.8    C         15.0     25.0   C         6.71     0.45   C       p
   5 │  1905-09-15 06:02:20.96    55.751   163.952     31.3      23.2     75.4    C         15.0     12.1   C         7.84     0.46   C       p       ⋯
                                                                                                                                     17 columns omitted

julia> tryparse.(Float64,isc[!, :smajax])
5-element Vector{Union{Nothing, Float64}}:
 17.8
 10.3
   nothing
 41.2
 31.3