diff --git a/CHANGELOG.md b/CHANGELOG.md
index 536c1adfe..a0d28f8a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,12 @@
 Changelog
 =========
 
+## 5.X.X (TBD)
+
+### Bug Fixes
+
+* Handle potential nil content value in RegisterErrorData class [#289](https://github.com/bugsnag/bugsnag-cocoa/pull/289)
+
 ## 5.15.6 (30 May 2018)
 
 ### Bug Fixes
diff --git a/Source/BugsnagCrashReport.m b/Source/BugsnagCrashReport.m
index 8d99b7aa1..273401e4a 100644
--- a/Source/BugsnagCrashReport.m
+++ b/Source/BugsnagCrashReport.m
@@ -630,9 +630,16 @@ + (instancetype)errorDataFromThreads:(NSArray *)threads {
             }
             NSString *contentValue = data[@"value"];
 
+#pragma clang diagnostic push
+#pragma ide diagnostic ignored "OCDFAInspection"
+            if (contentValue == nil || ![contentValue isKindOfClass:[NSString class]]) {
+                continue;
+            }
+#pragma clang diagnostic pop
+
             if ([self isReservedWord:contentValue]) {
                 reservedWord = contentValue;
-            } else if (!([[contentValue componentsSeparatedByString:@"/"] count] > 2)) {
+            } else if ([[contentValue componentsSeparatedByString:@"/"] count] <= 2) {
                 // must be a string that isn't a reserved word and isn't a filepath
                 [interestingValues addObject:contentValue];
             }
diff --git a/iOS/Bugsnag.xcodeproj/project.pbxproj b/iOS/Bugsnag.xcodeproj/project.pbxproj
index b1dfa9ef6..52ff718e0 100644
--- a/iOS/Bugsnag.xcodeproj/project.pbxproj
+++ b/iOS/Bugsnag.xcodeproj/project.pbxproj
@@ -312,6 +312,7 @@
 		F4295C14DCDDF541188CDE66 /* BugsnagSessionFileStore.h in Headers */ = {isa = PBXBuildFile; fileRef = F42955025DBE1DCEFD928CAA /* BugsnagSessionFileStore.h */; };
 		F4295C52A30DC98515F2FF02 /* BugsnagSessionTrackingApiClient.m in Sources */ = {isa = PBXBuildFile; fileRef = F4295FBD23F478FC6216A006 /* BugsnagSessionTrackingApiClient.m */; };
 		F4295DB3B395327B82A47A78 /* BugsnagSessionFileStore.m in Sources */ = {isa = PBXBuildFile; fileRef = F42954ACC6FFDDE3C8471495 /* BugsnagSessionFileStore.m */; };
+		F4295F017754324FD52CCE46 /* RegisterErrorDataTest.m in Sources */ = {isa = PBXBuildFile; fileRef = F42954B7D892334E7551F0F3 /* RegisterErrorDataTest.m */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -589,6 +590,7 @@
 		F429517A5571A61A897E963D /* BugsnagSessionTrackingApiClient.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = BugsnagSessionTrackingApiClient.h; path = ../Source/BugsnagSessionTrackingApiClient.h; sourceTree = SOURCE_ROOT; };
 		F42953E7E61199381E0405CC /* BugsnagFileStore.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = BugsnagFileStore.h; path = ../Source/BugsnagFileStore.h; sourceTree = SOURCE_ROOT; };
 		F42954ACC6FFDDE3C8471495 /* BugsnagSessionFileStore.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = BugsnagSessionFileStore.m; path = ../Source/BugsnagSessionFileStore.m; sourceTree = SOURCE_ROOT; };
+		F42954B7D892334E7551F0F3 /* RegisterErrorDataTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = RegisterErrorDataTest.m; sourceTree = "<group>"; };
 		F42955025DBE1DCEFD928CAA /* BugsnagSessionFileStore.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = BugsnagSessionFileStore.h; path = ../Source/BugsnagSessionFileStore.h; sourceTree = SOURCE_ROOT; };
 		F429554A50F3ABE60537F70E /* BugsnagKSCrashSysInfoParserTest.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = BugsnagKSCrashSysInfoParserTest.m; sourceTree = "<group>"; };
 		F42958B2E67C338E3086EAC2 /* BugsnagFileStore.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = BugsnagFileStore.m; path = ../Source/BugsnagFileStore.m; sourceTree = SOURCE_ROOT; };
@@ -726,6 +728,7 @@
 				8A2C8F951C6BC08600846019 /* report.json */,
 				8A2C8F291C6BBD2300846019 /* TestsInfo.plist */,
 				F429554A50F3ABE60537F70E /* BugsnagKSCrashSysInfoParserTest.m */,
+				F42954B7D892334E7551F0F3 /* RegisterErrorDataTest.m */,
 			);
 			name = Tests;
 			path = BugsnagTests;
@@ -1237,6 +1240,7 @@
 				E78C1EF31FCC615400B976D3 /* BugsnagSessionTrackingPayloadTest.m in Sources */,
 				E78C1EF11FCC2F1700B976D3 /* BugsnagSessionTrackerTest.m in Sources */,
 				F4295995C3259BF7D9730BC4 /* BugsnagKSCrashSysInfoParserTest.m in Sources */,
+				F4295F017754324FD52CCE46 /* RegisterErrorDataTest.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
diff --git a/iOS/BugsnagTests/RegisterErrorDataTest.m b/iOS/BugsnagTests/RegisterErrorDataTest.m
new file mode 100644
index 000000000..c302835a9
--- /dev/null
+++ b/iOS/BugsnagTests/RegisterErrorDataTest.m
@@ -0,0 +1,262 @@
+//
+// Created by Jamie Lynch on 11/06/2018.
+// Copyright (c) 2018 Bugsnag. All rights reserved.
+//
+
+
+#import <Foundation/Foundation.h>
+#import <XCTest/XCTest.h>
+
+@interface RegisterErrorData
++ (instancetype)errorDataFromThreads:(NSArray *)threads;
+@property (nonatomic, strong) NSString *errorClass;
+@property (nonatomic, strong) NSString *errorMessage;
+@end
+
+@interface RegisterErrorDataTest : XCTestCase
+@end
+
+@implementation RegisterErrorDataTest
+
+
+- (void)testNilAddresses {
+    XCTAssertNil([RegisterErrorData errorDataFromThreads:nil]);
+}
+
+- (void)testEmptyAddresses {
+    XCTAssertNil([RegisterErrorData errorDataFromThreads:@[]]);
+}
+
+- (void)testEmptyCrashedThreadDict {
+    NSDictionary *thread = @{
+            @"crashed": @YES
+    };
+    XCTAssertNil([RegisterErrorData errorDataFromThreads:@[thread]]);
+}
+
+- (void)testEmptyNotableAddresses {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{}
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNil(data);
+}
+
+- (void)testEmptyContentValue {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{}
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNil(data);
+}
+
+- (void)testNilValueImplicit {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNil(data);
+}
+
+- (void)testNilValueExplicit {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": [NSNull null]
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNil(data);
+}
+
+- (void)testHasTypeAndValue{
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"Hello, World!"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNil(data);
+}
+
+- (void)testFatalError {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNotNil(data);
+    XCTAssertEqualObjects(@"fatal error", data.errorClass);
+    XCTAssertEqualObjects(@"", data.errorMessage);
+}
+
+- (void)testAssertionFailed {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"assertion failed"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNotNil(data);
+    XCTAssertEqualObjects(@"assertion failed", data.errorClass);
+    XCTAssertEqualObjects(@"", data.errorMessage);
+}
+
+- (void)testPreconditionFailed {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"precondition failed"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertNotNil(data);
+    XCTAssertEqualObjects(@"precondition failed", data.errorClass);
+    XCTAssertEqualObjects(@"", data.errorMessage);
+}
+
+- (void)testSingleMessageValue {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    },
+                    @"message": @{
+                            @"type": @"string",
+                            @"value": @"Single Message"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertEqualObjects(@"Single Message", data.errorMessage);
+}
+
+- (void)testMultiMessageValue {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    },
+                    @"message": @{
+                            @"type": @"string",
+                            @"value": @"A is for aardvark"
+                    },
+                    @"message2": @{
+                            @"type": @"string",
+                            @"value": @"Z is for zebra"
+                    },
+                    @"message3": @{
+                            @"type": @"string",
+                            @"value": @"C is for crayfish"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertEqualObjects(@"A is for aardvark | C is for crayfish | Z is for zebra", data.errorMessage);
+}
+
+- (void)testStackExcluded {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    },
+                    @"message": @{
+                            @"type": @"stack",
+                            @"value": @"0xf0924501"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertEqualObjects(@"", data.errorMessage);
+}
+
+- (void)testOtherTypesExcluded {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    },
+                    @"message": @{
+                            @"type": @"someOtherType",
+                            @"value": @"do not serialise"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertEqualObjects(@"", data.errorMessage);
+}
+
+- (void)testFilepathExcluded {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    },
+                    @"message": @{
+                            @"type": @"string",
+                            @"value": @"/usr/share/locale"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertEqualObjects(@"", data.errorMessage);
+}
+
+- (void)testForwardSlashIncluded {
+    NSDictionary *thread = @{
+            @"crashed": @YES,
+            @"notable_addresses": @{
+                    @"hello_world": @{
+                            @"type": @"string",
+                            @"value": @"fatal error"
+                    },
+                    @"message": @{
+                            @"type": @"string",
+                            @"value": @"usr/share"
+                    }
+            }
+    };
+    RegisterErrorData *data = [RegisterErrorData errorDataFromThreads:@[thread]];
+    XCTAssertEqualObjects(@"usr/share", data.errorMessage);
+}
+
+@end