microg/GmsCore · error · IllegalArgumentException

Not a boolean type

Error message

Not a boolean type

What it means

Flag.getBool() throws IllegalArgumentException("Not a boolean type") when the flag's dataType is not DATA_TYPE_BOOL. Flag is a tagged union of primitive types, and each accessor guards its field with the type discriminator. Reading the boolean field of a non-boolean flag is rejected rather than returning a bogus default.

Source

Thrown at play-services-phenotype/src/main/java/com/google/android/gms/phenotype/Flag.java:77

    }

    public Flag(String name, byte[] bytesValue, int flagType) {
        this.name = name;
        this.bytesValue = bytesValue;
        this.dataType = DATA_TYPE_BYTES;
        this.flagType = flagType;
    }

    public long getLong() {
        if (dataType == DATA_TYPE_LONG)
            return longValue;
        throw new IllegalArgumentException("Not a long type");
    }

    public boolean getBool() {
        if (dataType == DATA_TYPE_BOOL)
            return boolValue;
        throw new IllegalArgumentException("Not a boolean type");
    }

    public double getDouble() {
        if (dataType == DATA_TYPE_DOUBLE)
            return doubleValue;
        throw new IllegalArgumentException("Not a double type");
    }

    public String getString() {
        if (dataType == DATA_TYPE_STRING)
            return stringValue;
        throw new IllegalArgumentException("Not a String type");
    }

    public byte[] getBytes() {
        if (dataType == DATA_TYPE_BYTES)
            return bytesValue;
        throw new IllegalArgumentException("Not a bytes type");

View on GitHub (pinned to 157c9d86ac)

Solutions

1. Guard with flag.getDataType() == Flag.DATA_TYPE_BOOL before calling getBool()
2. Switch over the DATA_TYPE_* constants and dispatch to the correct typed getter
3. Verify the server-side flag is still defined as a boolean experiment
4. Catch IllegalArgumentException at untrusted deserialization boundaries

Example fix

// before
boolean enabled = flag.getBool();
// after
boolean enabled = flag.getDataType() == Flag.DATA_TYPE_BOOL && flag.getBool();

if (flag.getDataType() != Flag.DATA_TYPE_BOOL) { throw new IllegalStateException("flag is not a bool: " + flag.getDataType()); }

static boolean isBoolFlag(Flag f) { return f != null && f.getDataType() == Flag.DATA_TYPE_BOOL; }

try { boolean v = flag.getBool(); } catch (IllegalArgumentException e) { log.warn("Flag type mismatch", e); v = DEFAULT_BOOL; }

When it happens

Trigger: Calling Flag.getBool() on a Flag whose dataType is DATA_TYPE_LONG (1), DATA_TYPE_DOUBLE (3), DATA_TYPE_STRING (4), or DATA_TYPE_BYTES (5) instead of DATA_TYPE_BOOL (2).

Common situations: Assuming all experiment flags of a given name are booleans after a server-side type change; iterating flag collections without a type switch; restoring flags from a Bundle where the type byte was lost or mis-set.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Not a long type
• Not a double type
• Not a String type
• Not a bytes type
• remoteBinder is the wrong class.

AI-assisted analysis of microg/GmsCore@157c9d86ac (2026-09-06). Data as JSON: /api/errors/39d4846be91994b9. Report an issue: GitHub.