diff --git a/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt b/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt
index 106f232..d7d8ed5 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/addsite/AddSiteViewModel.kt
@@ -153,7 +153,7 @@ class AddSiteViewModel(
         validationArgs = getValidationArgs(),
         networkTimeout = timeout,
         disabled = false,
-        certificate = certificateUri.value.toString()
+        certificate = certificateUri.value?.toString()
     )
 
     val newLastResult = ValidationResult(
diff --git a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt
index bc910b9..f41a9a7 100644
--- a/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt
+++ b/app/src/main/java/com/afollestad/nocknock/ui/viewsite/ViewSiteViewModel.kt
@@ -231,7 +231,7 @@ class ViewSiteViewModel(
         validationArgs = getValidationArgs(),
         networkTimeout = timeout,
         disabled = false,
-        certificate = certificateUri.value.toString()
+        certificate = certificateUri.value?.toString()
     )
 
     val retryPolicyTimes = retryPolicyTimes.value ?: 0
diff --git a/common/src/main/java/com/afollestad/nocknock/utilities/ext/StringExt.kt b/common/src/main/java/com/afollestad/nocknock/utilities/ext/StringExt.kt
index 2fa66dc..1256a27 100644
--- a/common/src/main/java/com/afollestad/nocknock/utilities/ext/StringExt.kt
+++ b/common/src/main/java/com/afollestad/nocknock/utilities/ext/StringExt.kt
@@ -18,3 +18,10 @@ package com.afollestad.nocknock.utilities.ext
 import android.net.Uri
 
 fun String.toUri() = Uri.parse(this)!!
+
+fun String?.isNotNullOrEmpty(): Boolean {
+  if (this == null || this == "null") {
+    return false
+  }
+  return !isNullOrEmpty()
+}
diff --git a/engine/src/main/java/com/afollestad/nocknock/engine/validation/ValidationExecutor.kt b/engine/src/main/java/com/afollestad/nocknock/engine/validation/ValidationExecutor.kt
index a9fb397..8ccbb1c 100644
--- a/engine/src/main/java/com/afollestad/nocknock/engine/validation/ValidationExecutor.kt
+++ b/engine/src/main/java/com/afollestad/nocknock/engine/validation/ValidationExecutor.kt
@@ -26,6 +26,7 @@ import com.afollestad.nocknock.data.model.Status.OK
 import com.afollestad.nocknock.engine.R
 import com.afollestad.nocknock.engine.ssl.SslManager
 import com.afollestad.nocknock.engine.validation.ValidationJob.Companion.KEY_SITE_ID
+import com.afollestad.nocknock.utilities.ext.isNotNullOrEmpty
 import com.afollestad.nocknock.utilities.providers.BundleProvider
 import com.afollestad.nocknock.utilities.providers.JobInfoProvider
 import com.afollestad.nocknock.utilities.providers.StringProvider
@@ -168,7 +169,7 @@ class RealValidationExecutor(
 
     return try {
       val clientWithTimeout = clientTimeoutChanger(okHttpClient, siteSettings.networkTimeout)
-      val client = if (!siteSettings.certificate.isNullOrEmpty()) {
+      val client = if (siteSettings.certificate.isNotNullOrEmpty()) {
         sslManager.clientForCertificate(
             certUri = siteSettings.certificate!!,
             siteUri = site.url,
@@ -205,6 +206,7 @@ class RealValidationExecutor(
           )
       )
     } catch (ex: Exception) {
+      ex.printStackTrace()
       log("performValidation(${site.id}) = Error: ${ex.message}")
       CheckResult(model = site.withStatus(status = ERROR, reason = ex.message))
     }