fix: Fix issue with IronFox giving 400 error

app/src/main/kotlin/com/looker/droidify/network/header/KtorHeadersBuilder.kt

@@ -10,9 +10,10 @@ internal class KtorHeadersBuilder(
 ) : HeadersBuilder {
 
     override fun String.headsWith(value: Any?) {
-        if (value == null) return
+        val stringValue = value?.toString()
+        if (stringValue.isNullOrBlank()) return
         with(builder) {
-            append(this@headsWith, value.toString())
+            append(this@headsWith, stringValue)
         }
     }
 

app/src/test/kotlin/com/looker/droidify/network/header/KtorHeadersBuilderTest.kt

@@ -0,0 +1,51 @@
+package com.looker.droidify.network.header
+
+import io.ktor.http.HeadersBuilder
+import io.ktor.http.HttpHeaders
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class KtorHeadersBuilderTest {
+
+    private fun build(block: KtorHeadersBuilder.() -> Unit): io.ktor.http.Headers {
+        val builder = HeadersBuilder()
+        KtorHeadersBuilder(builder).block()
+        return builder.build()
+    }
+
+    @Test
+    fun `blank values are not appended`() {
+        val headers = build {
+            ifModifiedSince("")
+            etag("")
+            authentication("")
+        }
+        assertFalse(headers.contains(HttpHeaders.IfModifiedSince))
+        assertFalse(headers.contains(HttpHeaders.ETag))
+        assertFalse(headers.contains(HttpHeaders.Authorization))
+    }
+
+    @Test
+    fun `null values are not appended`() {
+        val headers = build {
+            HttpHeaders.IfModifiedSince headsWith null
+            HttpHeaders.ETag headsWith null
+            HttpHeaders.Authorization headsWith null
+        }
+        assertTrue(headers.isEmpty())
+    }
+
+    @Test
+    fun `non-blank values are appended`() {
+        val headers = build {
+            ifModifiedSince("Thu, 02 Jul 2026 05:43:42 GMT")
+            etag("\"73ff6c74615547729ecedd240ad9f01d\"")
+            authentication("Basic dXNlcjpwYXNz")
+        }
+        assertEquals("Thu, 02 Jul 2026 05:43:42 GMT", headers[HttpHeaders.IfModifiedSince])
+        assertEquals("\"73ff6c74615547729ecedd240ad9f01d\"", headers[HttpHeaders.ETag])
+        assertEquals("Basic dXNlcjpwYXNz", headers[HttpHeaders.Authorization])
+    }
+}