Incorrect documentation for null values conversion in to-number expression.

[sharkinsspatial]

mapbox-gl-js version: 0.47.0

browser: Chrome 67.0.3396.87

Steps to Trigger Behavior

1. Apply filter expression to a source where the property used in the get expression does not exist for the feature.
2. Use a to-number expression to convert the null value to 0.

Link to Demonstration

jsFiddle (please open devTools to see relevant console warnings).

Expected Behavior

Non-existent property value should be converted to 0 as described in the to-number documentation.

Actual Behavior

A console warning Could not convert null to number. is created.

I am using this approach in filter expressions as described in this issue. It also appears that the existing tests contradict the to-number null value handling described in the documentation.

[jfirebaugh]

Good catch. I'm not sure whether the documentation or implementation is in error. /cc @anandthakker

[anandthakker]

Ah. Yeah, IIRC the documentation states our original intent, and I still think that makes sense.

[Sillson]

Question about the behavior if someone has a moment to answer --

If the the "to-number" function returns 0 from null, doesn't this conflict with parsing a string of '0'? Fore example, if I'm hoping to conditionally style in the following way:

'paint': {
      'circle-color': [
        'case',
          ['all', [">=", ["to-number", ["get", "value"]], 0], ["<", ["to-number", ["get", "value"]], 100]], '#fff',
          ['all', [">=", ["to-number", ["get", "value"]], 100], ["<", ["to-number", ["get", "value"]], 500]], '#000',
          "#2f2f2f"
      ]
    },

This means both my null and '0' values return 0.

[dhaq]

Did you resolved this issues on iOS?