Fix d3.geo.bounds for null geometries.

This fixes an error that would be thrown if no defined bounds were
found.  It also ensures that undefined bounds are returned as
[[NaN, NaN], [NaN, NaN]], for consistency with d3.extent, which returns
[undefined, undefined] for an empty array.

Fixes #1154.

d3.js

@@ -2259,8 +2259,10 @@ d3 = function() {
       φ1 = λ1 = -(λ0 = φ0 = Infinity);
       ranges = [];
       d3.geo.stream(feature, bound);
+      var n = ranges.length;
+      if (n) {
         ranges.sort(compareRanges);
-      for (var i = 1, n = ranges.length, a = ranges[0], b, merged = [ a ]; i < n; ++i) {
+        for (var i = 1, a = ranges[0], b, merged = [ a ]; i < n; ++i) {
           b = ranges[i];
           if (withinRange(b[0], a) || withinRange(b[1], a)) {
             if (angle(a[0], b[1]) > angle(a[0], a[1])) a[1] = b[1];
@@ -2274,8 +2276,9 @@ d3 = function() {
           b = merged[i];
           if ((dλ = angle(a[1], b[0])) > best) best = dλ, λ0 = b[0], λ1 = a[1];
         }
+      }
       ranges = range = null;
-      return [ [ λ0, φ0 ], [ λ1, φ1 ] ];
+      return λ0 === Infinity || φ0 === Infinity ? [ [ NaN, NaN ], [ NaN, NaN ] ] : [ [ λ0, φ0 ], [ λ1, φ1 ] ];
     };
   }();
   d3.geo.centroid = function(object) {

src/geo/bounds.js

@@ -136,11 +136,13 @@ d3.geo.bounds = (function() {
 
     d3.geo.stream(feature, bound);
 
+    var n = ranges.length;
+    if (n) {
       // First, sort ranges by their minimum longitudes.
       ranges.sort(compareRanges);
 
       // Then, merge any ranges that overlap.
-    for (var i = 1, n = ranges.length, a = ranges[0], b, merged = [a]; i < n; ++i) {
+      for (var i = 1, a = ranges[0], b, merged = [a]; i < n; ++i) {
         b = ranges[i];
         if (withinRange(b[0], a) || withinRange(b[1], a)) {
           if (angle(a[0], b[1]) > angle(a[0], a[1])) a[1] = b[1];
@@ -157,8 +159,11 @@ d3.geo.bounds = (function() {
         b = merged[i];
         if ((dλ = angle(a[1], b[0])) > best) best = dλ, λ0 = b[0], λ1 = a[1];
       }
+    }
     ranges = range = null;
 
-    return [[λ0, φ0], [λ1, φ1]];
+    return λ0 === Infinity || φ0 === Infinity
+        ? [[NaN, NaN], [NaN, NaN]]
+        : [[λ0, φ0], [λ1, φ1]];
   };
 })();

test/geo/bounds-test.js

@@ -228,6 +228,36 @@ suite.addBatch({
           }
         ]
       }), [[-120,46], [-119,47]]);
+    },
+    "null geometries": {
+      "Feature": function(bounds) {
+        var b = bounds({type: "Feature", geometry: null});
+        assert.isNaN(b[0][0]);
+        assert.isNaN(b[0][1]);
+        assert.isNaN(b[1][0]);
+        assert.isNaN(b[1][1]);
+      },
+      "MultiPoint": function(bounds) {
+        var b = bounds({type: "MultiPoint", coordinates: []});
+        assert.isNaN(b[0][0]);
+        assert.isNaN(b[0][1]);
+        assert.isNaN(b[1][0]);
+        assert.isNaN(b[1][1]);
+      },
+      "MultiLineString": function(bounds) {
+        var b = bounds({type: "MultiLineString", coordinates: []});
+        assert.isNaN(b[0][0]);
+        assert.isNaN(b[0][1]);
+        assert.isNaN(b[1][0]);
+        assert.isNaN(b[1][1]);
+      },
+      "MultiPolygon": function(bounds) {
+        var b = bounds({type: "MultiPolygon", coordinates: []});
+        assert.isNaN(b[0][0]);
+        assert.isNaN(b[0][1]);
+        assert.isNaN(b[1][0]);
+        assert.isNaN(b[1][1]);
+      }
     }
   }
 });