Do not throw an error since broken prev map is popular issue

lib/source-map-generator.js

@@ -107,7 +107,9 @@ SourceMapGenerator.prototype.addMapping =
     var name = util.getArg(aArgs, 'name', null);
 
     if (!this._skipValidation) {
-      this._validateMapping(generated, original, source, name);
+      if (this._validateMapping(generated, original, source, name) === false) {
+        return;
+      }
     }
 
     if (source != null) {
@@ -273,11 +275,14 @@ SourceMapGenerator.prototype._validateMapping =
     // specific error message to try to guide them the right way.
     // For example: https://github.com/Polymer/polymer-bundler/pull/519
     if (aOriginal && typeof aOriginal.line !== 'number' && typeof aOriginal.column !== 'number') {
-        throw new Error(
+      if (typeof console !== 'undefined' && console.warn) {
+        console.warn(
             'original.line and original.column are not numbers -- you probably meant to omit ' +
             'the original mapping entirely and only map the generated position. If so, pass ' +
             'null for the original mapping instead of an object with empty or null values.'
         );
+      }
+      return false;
     }
 
     if (aGenerated && 'line' in aGenerated && 'column' in aGenerated
@@ -295,12 +300,15 @@ SourceMapGenerator.prototype._validateMapping =
       return;
     }
     else {
-      throw new Error('Invalid mapping: ' + JSON.stringify({
-        generated: aGenerated,
-        source: aSource,
-        original: aOriginal,
-        name: aName
-      }));
+      if (typeof console !== 'undefined' && console.warn) {
+        console.warn('Invalid mapping: ' + JSON.stringify({
+          generated: aGenerated,
+          source: aSource,
+          original: aOriginal,
+          name: aName
+        }));
+      }
+      return false;
     }
   };
 

test/test-source-map-generator.js

@@ -85,14 +85,6 @@ exports['test adding mappings (invalid)'] = function (assert) {
   assert.throws(function () {
     map.addMapping({});
   });
-
-  // Original file position, but no source.
-  assert.throws(function () {
-    map.addMapping({
-      generated: { line: 1, column: 1 },
-      original: { line: 1, column: 1 }
-    });
-  });
 };
 
 exports['test adding mappings with skipValidation'] = function (assert) {