Fixed {{price}} helper to render empty instead of throwing

refs https://github.com/TryGhost/Toolbox/issues/497
refs fb7532bf5d

- We downgraded the 'GS090-NO-PRICE-DATA-CURRENCY-CONTEXT' rule in gscan to non-fatal, meaning Ghost should not be throwing an error but instead render an empty value for {{price}} helper when price data is empty.
- For example, a legacy syntax like this: '{{price currency=@price.currency}}' should not cause a page render error but return an empty price string.
- The pattern of returning an empty string instead of crashing is used in other helpers like {{img_url}} and and {{url}}

ghost/core/core/frontend/helpers/price.js

@@ -8,10 +8,10 @@
 // Usage: `{{price 500 currency="USD"}}`
 // Usage: `{{price currency="USD"}}`
 //
-// Returns amount equal to the dominant denomintation of the currency.
+// Returns amount equal to the dominant denomination of the currency.
 // For example, if 2100 is passed, it will return 21.
-const errors = require('@tryghost/errors');
 const tpl = require('@tryghost/tpl');
+const logging = require('@tryghost/logging');
 const _ = require('lodash');
 
 const messages = {
@@ -82,22 +82,19 @@ module.exports = function price(planOrAmount, options) {
 
     // CASE: if no amount is passed, e.g. `{{price}}` we throw an error
     if (arguments.length < 2) {
-        throw new errors.IncorrectUsageError({
+        logging.warn(tpl(messages.attrIsRequired));
-            message: tpl(messages.attrIsRequired)
+        return '';
-        });
     }
 
     // CASE: if amount is passed, but it is undefined we throw an error
     if (amount === undefined) {
-        throw new errors.IncorrectUsageError({
+        logging.warn(tpl(messages.attrIsRequired));
-            message: tpl(messages.attrIsRequired)
+        return '';
-        });
     }
 
     if (!_.isNumber(amount)) {
-        throw new errors.IncorrectUsageError({
+        logging.warn(tpl(messages.attrMustBeNumeric));
-            message: tpl(messages.attrMustBeNumeric)
+        return '';
-        });
     }
 
     return amount / 100;

ghost/core/test/unit/frontend/helpers/price.test.js

@@ -1,9 +1,21 @@
-const should = require('should');
+const sinon = require('sinon');
 const price = require('../../../../core/frontend/helpers/price');
 
-const {registerHelper, shouldCompileToError, shouldCompileToExpected} = require('./utils/handlebars');
+const {registerHelper, shouldCompileToExpected} = require('./utils/handlebars');
+
+const logging = require('@tryghost/logging');
 
 describe('{{price}} helper', function () {
+    let logWarnStub;
+
+    beforeEach(function () {
+        logWarnStub = sinon.stub(logging, 'warn');
+    });
+
+    afterEach(function () {
+        sinon.restore();
+    });
+
     before(function () {
         registerHelper('price');
     });
@@ -11,24 +23,22 @@ describe('{{price}} helper', function () {
     it('throws an error for no provided parameters', function () {
         const templateString = '{{price}}';
 
-        shouldCompileToError(templateString, {}, {
+        shouldCompileToExpected(templateString, {}, '');
-            name: 'IncorrectUsageError'
+        logWarnStub.calledOnce.should.be.true();
-        });
     });
 
     it('throws an error for undefined parameter', function () {
         const templateString = '{{price @dont.exist}}';
 
-        shouldCompileToError(templateString, {}, {
+        shouldCompileToExpected(templateString, {}, '');
-            name: 'IncorrectUsageError'
+        logWarnStub.calledOnce.should.be.true();
-        });
     });
 
     it('throws if argument is not a number', function () {
         const templateString = '{{price "not_a_number"}}';
-        shouldCompileToError(templateString, {}, {
+
-            name: 'IncorrectUsageError'
+        shouldCompileToExpected(templateString, {}, '');
-        });
+        logWarnStub.calledOnce.should.be.true();
     });
 
     it('will format decimal adjusted amount', function () {