[WW-5125] use .get(...) instead of [...] for fieldErrors

All [ occurrences in all ftl files reviewed. Only fieldErrors had used [...] which replaced by .get(...) to fix WW-5125 as well as aligning with other ftl files conduct.

apps/showcase/src/main/resources/template/ajaxErrorContainers/controlfooter.ftl

@@ -22,12 +22,12 @@ ${parameters.after!}<#t/>
     </td><#lt/>
 </tr>
 <#if (parameters.errorposition!"top") == 'bottom'>
-<#assign hasFieldErrors = parameters.name?? && fieldErrors?? && fieldErrors[parameters.name]??/>
+<#assign hasFieldErrors = parameters.name?? && fieldErrors?? && fieldErrors.get(parameters.name)??/>
 <#if hasFieldErrors>
 <tr errorFor="${parameters.id}">
     <td class="tdErrorMessage" colspan="2"><#rt/>
         <#if hasFieldErrors>
-            <#list fieldErrors[parameters.name] as error>
+            <#list fieldErrors.get(parameters.name) as error>
                 <div class="errorMessage">${error}</div><#t/>
             </#list>
         </#if>

apps/showcase/src/main/resources/template/ajaxErrorContainers/controlheader-core.ftl

@@ -21,12 +21,12 @@
 <#--
 	Always include elements to show errors. They may be filled later via AJAX.
 -->
-<#assign hasFieldErrors = parameters.name?? && fieldErrors?? && fieldErrors[parameters.name]??/>
+<#assign hasFieldErrors = parameters.name?? && fieldErrors?? && fieldErrors.get(parameters.name)??/>
 <#if (parameters.errorposition!"top") == 'top'>
 <tr errorFor="${parameters.id}">
     <td class="tdErrorMessage" colspan="2" data-error-for-fieldname="${parameters.name}"><#rt/>
         <#if hasFieldErrors>
-            <#list fieldErrors[parameters.name] as error>
+            <#list fieldErrors.get(parameters.name) as error>
                 <div class="errorMessage">${error}</div><#t/>
             </#list>
         </#if>