magento#7241: No option to start with blank option for prefix and suffix in checkout.

 - replace usage of empty string for optional value with space so that the knockout.js picks up the optional values

Author: dmanners

app/code/Magento/Customer/Block/Widget/Name.php

@@ -106,8 +106,11 @@ public function getPrefixOptions()
         $prefixOptions = $this->options->getNamePrefixOptions();
 
         if ($this->getObject() && !empty($prefixOptions)) {
-            $oldPrefix = $this->escapeHtml(trim($this->getObject()->getPrefix()));
-            $prefixOptions[$oldPrefix] = $oldPrefix;
+            $prefixOption = $this->getObject()->getPrefix();
+            $oldPrefix = $this->escapeHtml(trim($prefixOption));
+            if ($prefixOption !== null && !isset($prefixOptions[$oldPrefix]) && !isset($prefixOptions[$prefixOption])) {
+                $prefixOptions[$oldPrefix] = $oldPrefix;
+            }
         }
         return $prefixOptions;
     }
@@ -161,8 +164,11 @@ public function getSuffixOptions()
     {
         $suffixOptions = $this->options->getNameSuffixOptions();
         if ($this->getObject() && !empty($suffixOptions)) {
-            $oldSuffix = $this->escapeHtml(trim($this->getObject()->getSuffix()));
-            $suffixOptions[$oldSuffix] = $oldSuffix;
+            $suffixOption = $this->getObject()->getSuffix();
+            $oldSuffix = $this->escapeHtml(trim($suffixOption));
+            if ($suffixOption !== null && !isset($suffixOptions[$oldSuffix]) && !isset($suffixOptions[$suffixOption])) {
+                $suffixOptions[$oldSuffix] = $oldSuffix;
+            }
         }
         return $suffixOptions;
     }

app/code/Magento/Customer/Model/Options.php

@@ -92,13 +92,14 @@ private function prepareNamePrefixSuffixOptions($options, $isOptional = false)
         }
         $result = [];
         $options = explode(';', $options);
-        if ($isOptional && trim(current($options))) {
-            array_unshift($options, '');
-        }
         foreach ($options as $value) {
             $value = $this->escaper->escapeHtml(trim($value));
             $result[$value] = $value;
         }
+        if ($isOptional && trim(current($options))) {
+            $result = array_merge([' ' => ' '], $result);
+        }
+
         return $result;
     }
 }